Paper - Development and transition of the testis, normal and abnormal 2
|Embryology - 9 Dec 2023 Expand to Translate|
|Google Translate - select your language from the list shown below (this will open a new external page)|
العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt These external translations are automated and may not be accurate. (More? About Translations)
Lockwood CB. Development and transition of the testis, normal and abnormal. (1887) J Anat. 22(1): 38-77. PMID 17231729
|Historic Disclaimer - information about historic embryology pages|
|Embryology History | Historic Embryology Papers)|
The Development and Transition of the Testis, Normal and Abnormal
By C. B.Lockwood, F.R.C.S., Hunterian Professor of Comparative Anatomy and Physiology, Royal College of Surgeons of England. (Puate II.)
(Continued from vol, xxi. p. 664.)
Glomeruli of Wolffian Body
The glomeruli of the Wolffian body have been frequently referred to in the first Lecture, but, so far, nothing has been said concerning their histology or development. This omission may now be repaired, and, fortunately, suitable human embryos are available for the purpose. This happens because the glomeruli have just appeared in the youngest human embryo at my disposal, and are still in their most primitive condition. In order of development the glomeruli are not manifest until after the Wolffian duct and tubules are well established; and, roughly speaking, their appearance coincides with the earliest budding of the limbs; but, preparatory to their development the Wolffian tubules grow and alter. It may be best to glance for a moment at that phenomenon, and then proceed with the development of the glomeruli.
In Lecture I. the development of the Wolffian tubules was traced until they looked as if they were hollow outgrowths from the duct, and in this early stage their length was insignificant, and they only reached from the inner side of the duct as far as the peritoneal epithelium. But afterwards the tubule elongates, and, by the time the glomerulus has appeared, is slightly bent. A typical tubule would consist of the following parts:—(1) a section carrying the peritoneal opening, and known as the peritoneal funnel,! (2) a dilated vesicle into which this opens, (8) a coiled tubulus proceeding from (2), and terminating in (4) a wider portion opening into the Wolffian duct.! Evidence has been adduced to show that the human embryo, as well as the rabbit, has at the fore end of its Wolffian body peritoneal openings or nephrostomata, but these will not be mentioned again, because this portion of the organ totally disappears, and has nothing whatever to do with the events which follow. But the tubules do not present, either in the rabbit or in the human embryo, any peculiarity at their opening into the Wolffian duct; but towards its other extremity there is a dilatation, into which a bunch of capillaries grows to form a glomerulus. It therefore follows that all the human embryo ultimately possesses of the four divisions of a typical tubule is (1) a coiled canal and (2) its dilated glomeruluscontaining part. But we must not forget that in one of the transverse sections of a human embryo of the thirtieth day of intrauterine life a very strong resemblance to the typical arrangement can be traced (fig. 19, Pl. XV. Lecture I.). In this case the tubule running from the peritoneal epithelium and ending at a large glomerulus is of the greatest significance, and seems to represent a “peritoneal funnel.” Before describing the development of the glomeruli, the manner of growth of the tubule calls for inquiry, and at the outset it is clear that it can hardly take place by additions made at either end. As far as can be judged, the cells which form its walls divide and multiply, and in so doing increase both the length and calibre of the canal they surround.
1 Foster and Balfour, 2nd edit. p. 193. atttisg , obser F Huth, Lith? Edin?
1 Since the first lecture was published, I have seen an exceedingly wide opening between a Wolffian tubule and the pleuro-peritoneal cavity in a rabbit’s embryo of 9 days and 18 hours,
Taking both the pronephros and mesonephros into consideration, two sorts of glomeruli may be developed in connection with them. The first variety are called external glomeruli, because they protrude into the pleuro-peritoneal cavity instead of into the tubules. Their presence is undoubted in the chick, but it is very questionable whether they exist in the rabbit, and in man their development has hardly been established, although I have described a specimen in which it is possible that they have been imitated. However, in the absence of confirmatory evidence, it would be rash to aver their existence upon such grounds as these, and therefore, under the circumstances, only the other kind of glomeruli remain for examination. In contradistinction to those which have just been mentioned these are named “internal glomeruli,” and they protrude into the Wolffian tubules, A perusal of Mr Sedgwick’s! monograph shows that the distinction is rather one of detail than of principle, because that author satisfactorily shows that the external glomeruh are simply internal glomeruli which have protruded into the peritoneal cavity through greatly widened-out nephrostomata. However, the names are very convenient, and deserve to be retained. In future, for reasons which have just been given, only internal glomeruli are in question. The accompanying figure, made from a section of a human embryo at about the thirtieth day, affords an idea of the appearance of one of these structures shortly after its appearance. The canal of the Wolffian tubule is at this time about ,djth of an inch in diameter, but is dilated at the end which is furthest from the Wolffian duct to contain the glomerulus. The latter consists of capillaries surrounded by round mesoblastic cells (Pl. II. fig. 23), and covered, where it protrudes into the tubules, by a reflection of the lining epithelium, which consists of a single layer of cubical cells. In this specimen there is no histological difference between the cells which line the tubule, and its dilatation, and those which cover the glomerulus. At this early stage the glomerulus bulges prominently into the expanded tubule, and is continuous by a wide base with the rest of the mesoblast of the Wolffian body. However, a trace of a constriction has begun to form at the base, and this by its increase will afterwards form the “neck of the glomerulus.” The mesoblast, which in a great measure composes the Wolffian body and glomeruli, is embryonic in type and consists of round nucleated cells, which are about +-4,5th of an inch in diameter. These elements have indistinct margins, and in some parts protoplasmic processes unite adjoining cells. The blood-vessels of the Wolffian body at this stage are not very numerous, and are bounded by spindle-shaped cells; they run as loops into the glomeruli (fig. 23), Whatever histological changes take place after this, and they are many, the anatomical arrangement which has been described, a glomerulus protruding into the dilatation of a tubule, does not alter, except that the glomerulus, owing to a narrowing of its neck, becomes more pendent into the cavity which contains it (figs. 24 and 25). As regards the place at which the glomerulus protrudes into the tubule, it may be noted that the invagination is not exactly at the end of the tubule, but usually at one side. Of course such a trivial circumstance as this hardly alters the anatomical arrangement.
1 Adam Sedgwick, On Early Development of the Anterior Part of the Wolfian Duct and Body in the Chick, &c., p. 24.
After it has been established in this way, the glomerulus grows larger, and the tissues of which it is made assume new and altered characters, For instance, both im human embryos and in rabbits, the epithelium which covers its surface changes its cubical shape and becomes flattened. The cell nuclei do not participate in the change but remain round and plump, and bulge in a striking manner and clearly mark the margin of the glomerulus (fig. 25). The layer of epithelium which lines the interior of the glomerulus-containing sac, that which corresponds to Bowman’s capsule in the kidney, also becomes flattened, except where it joins the cubical epithelium of the tubule; here it retains its original form (fig. 24). Accompanying these changes in the epithelium are others in the substance of the glomerulus. It has been seen that at its first appearance the latter consisted of small round cells, a few of which were elongated and bounded the capillary loop. The human embryo which yielded this information was somewhere near the thirtieth day of intrauterine life and had but a slight degree of perfection. In another human embryo, §ths of an inch long and about the seventh week of intrauterine life (fig. 24, also fig. 39, p. 61), and in which the limbs and fingers and toes were clearly formed, the development of the glomeruli had advanced a step. During the early phases the epithelial covering was easy to recognise because of its cubical shape and deep staining, but in the seven weeks’ embryo its identity is by no means so clear, although, without doubt, it is represented by some slightly flattened cells which cover the surface. Moreover, the elements which form the bulk of the glomerulus are bigger than they were at the thirtieth day, and this seems due to an increase in the amount of the protoplasm which surrounds the nucleus. But, besides increasing in amount, it is perceptible that the protoplasm, especially that which belongs to the cells near the neck of the glomerulus, has sent out branches which, by joing with corresponding processes from other cells, are beginning to form a reticulated network ; this reticulum is of the greatest interest and importance, and will be mentioned again presently. However, the bulk of the glomerulus consists at this stage of rounded nucleated cells interpenetrated by a few capillaries, which seem to originate as follows :—Along certain routes the embryonic cells, both of the glomerulus and of the Wolffian body in general, elongate and arrange themselves in parallel lines, separated by a narrow interval into which blood from the neighbouring great vessel enters. Nothing could be simpler than this process, and after originating like this the vessels consist of an afferent set, running from the aorta to the glomerulus, and an efferent set, opening into the great vein of the Wolffian body, the posterior cardinal vein.
If such a glomerulus as that which has been described be compared with those of the kidney, with which every one is familiar, their want of perfection is manifest. We are therefore impelled to carry our inquiries further, and a human embryo whose body and head together measured 1??; inch long, and which had arrived somewhere near the tenth week of intrauterine life (fig. 40, p. 65), afforded a suitable opportunity. In thisembryo some of the glomeruli were as large as, if not larger than, those of the adult kidney, and their vascularity was remarkable (fig. 25). The whole glomerulus is composed of a complicated interlacement of tortuous capillaries, amongst which a few cells are intermingled ; and, moreover, the epithelial elements have deviated from their early cubical shape, so that both the surface of the glomerulus and the interior of its capsule are lined with flattened nucleated cells, By the time the glomeruli of the Wolffian body have reached this stage of development their resemblance to their fellows of the kidney is very obvious and needs no comment. However, the comparison has an additional interest, because it enables us to infer that the Wolffian glomerulus has reached the period of its greatest perfection. It will be shown presently that this is a stage at which few glomeruli are destined to arrive. Many of those which appear during the earliest, and greatest development of the Wolffian body participate in the atrophy which overtakes the foremost part of the organ, but this is a point which may be reserved for a little while.
Whilst the glomeruli have been passing through these phases of development the tubules and matrix have not remained quiescent. But, before speaking of these, it is important and interesting to ascertain how many tubules and glomeruli the human embryo may possess. Of course an exact determination is hardly possible, but in longitudinal sections of the youngest human embryo that has been mentioned in these pages (fig. 1, p. 637), and which was estimated to have arrived at the twenty-third day of intrauterine life, I calculate that from fifteen to sixteen tubules, and a like number of glomeruli, were present. In the longitudinal sections of another human embryo, also spoken of before, and estimated to have arrived somewhere near the thirtieth day (Pl. XV. figs. 21 and 22, Lect. I.), there seemed to be from eighteen to twenty tubules and glomeruli. The difference in these two cases is so small that it is evident that, assuming the ages are right, an inconsiderable, or possibly no new development of extra tubules or glomeruli takes place between the twentieth and the thirtieth day of intrauterine life. In a third human embryo which has been mentioned already (p. 39), and which was estimated to have reached nearly the seventh week of intrauterine life, it is hard to say whether the number of glomeruli and tubules has increased; although, on the contrary, some of the foremost, as will be described hereafter, have begun to atrophy (fig. 39, p. 61). The same holds good for a larger human embryo, previously mentioned (fig. 40, p. 65), and whose length was 1,4 inch, and whose age was thought to be about the tenth week of intrauterine life; in this specimen there is no ‘increase in the numbers of the glomeruli, but a greater perfection of some, and an atrophy of others. If these inferences are correct, it is clear that they establish a ditterence between the human embryo and that of the chick, for in the latter, as Foster and Balfour! point out,
“In addition to the primary tubules, secondary and tertiary tubules are formed on the dorsal side of the primary tubules. They are differentiated out of the mesoblast of the intermediate cell mass and open independently into the Wolffian duct.”
1 Foster and Balfour, 2nd edit., p. 192.
Judging from the number of openings into the Wolffian duct, it seems exceedingly doubtful whether in the human embryo any tubules are developed after those which have been described.
It follows, therefore, from what has gone before, that in the human embryo the glomeruli of the Wolffian body reach perfection at a comparatively early period, probably about the tenth week of intrauterine life, but even then some of those which are anterior have begun to atrophy, and it may be said in anticipation that this is the ultimate destiny of all of these structures. But before this interesting topic is touched, if the natural consequence of events is-kept in view, other circumstances claim attention, and foremost may be mentioned the relative positions of the various structures which compose the Wolffian body. The situation of the duct, tubule, and glomerulus are portrayed in fig. 2, Lect. I. p. 638, which represents a human embryo at about the twenty-eighth day, or in fig. 37, p. 48, which represents the Wolffian body and genital mass, or sexual eminence as the latter is sometimes ealled, of a rabbit of thirteen and a half days of intrauterine life. These drawings clearly show that the duct lies towards the extreme outer limit of the organ, that is to say, as far as possible away from the mesentery and aorta; the glomerulus, on the other hand, lies more towards the inner side and in front, so that it 1s quite near the base of the mesentery. It therefore follows that the duct and glomerulus are some distance apart, and this interval is occupied by the tortuous tubules. That part of the Wolffian body which is nearest the spine contains, as was said before, the vein (posterior cardinal) which carries away its effluent blood. It is desirable to make a careful note of these relations, because they help the interpretation of many subsequent events. A word may be said in this place concerning the lining epithelium of the various canals. In rabbits and in human embryos the Wolffian duct is lined with columnar ciliated epithelium during the later stages. The Wolffian tubules have also a lining of regularly arranged columnar cells, and the inner edge of the cells (fig. 37, p. 48) has large and irregular protoplasmic protrusions, After the seventeenth day in rabbits the cell lining of the tubules of the Wolffian body becomes less columnar and particularly like the epithelium which lines the convoluted tubules of the kidney.
Parenchyma of Wolffian Body
The only portions of the Wolffian body which have not been particularly mentioned are its epithelial covermg and the mesoblast which surrounds and imbeds the other elements. The latter has already been mentioned indirectly in connection with the connective tissue portion of the glomeruli, so that it is natural to complete the account of its development, Doubtless it is unnecessary to begin anew the description of the mesoblast which composes the human Wolffian body. At first it consists of round protoplasmic cells, each of which possesses a central nucleus. The process by which a very definite reticulated stroma is developed from the round nucleated cells is quite simple; their protoplasm sends out branches which unite with those of adjoining cells so that at last a nucleated meshwork is established. The various stages by which these alterations are brought about are shown in the accompanying figures (figs. 23, 24, and 25), which also indicate that, besides forming the reticulum, some of the eells are converted, in the manner which has been described, into the walls of the various capillaries and blood-vessels. Mere pictorial representations convey but a poor idea of the perfection and beauty of the tissue which forms the parenchyma of the Wolffian body, nor does comparison afford much assistance. Its resemblance to the so-called mucoid or gelatinous connective tissue,! so far as the meshwork is concerned, is palpable; but here the likeness ends. To complete the analogy it would be necessary to demonstrate the presence of mucin in the meshwork, and it is hard to tell how this could be accomplished. But, whatever the nature of the parenchyma of the Wolffian body may be, the tissue which constitutes it is not solely confined to that organ. The last embryo which has been described, that which was supposed to have attained the tenth week of intrauterine life, possesses kidneys of some perfection, and the various glomeruli and tubules which go to form the organ lie in an identical matrix. This observation is so much in accordance with the views usually entertained of the relationship which exists between the permanent kidneys and Wolffian bodies, that there is no difficulty in its acceptance; but in a little while it will be demonstrated, that by the time it has reached a certain stage of development, the body of the testis has a reticulum which differs in no material degree from the parenchyma of the organs which have just been mentioned, namely, of the kidney and of the Wolffian body. The importance of this statement, both from a developmental and from a pathological point of view, will be admitted when we consider that branch of our subject which treats of the development of the body of the testis, and the time has now arrived at which this task may be profitably and conveniently undertaken.
1 Vide Klein, Atlas of Histology, 1880, p. 88.
Development of the Body of the Testis
The mere origin of the body of the testis is a matter of general agreement. This point has been clearly determined in the chick and in many of the smaller mammals, and therefore, so far as they are concerned, the question does not call for lengthened notice. Under the circumstances it 1s proposed, as a preliminary, to endeavour to ascertain how the gland appears in rabbits and afterwards in human embryos. When once the origin of the testicle has been illustrated the development of its. various constituents will call for attention, and upon this branch of the subject the widest differences of opinion exist. It would be easy to verify this statement by reference to the well-known writings of Foster, Allen Thomson, or Balfour, or to the admirable epitome which Janosik gives in his recent memoir. As we proceed, the different views will be indicated, but at present let us confine ourselves to the question of the origin of the body of the testicle. At present it is a matter of common acceptation that, at their commencement, no one can discriminate between the rudiments of the ovary and those of the testicle, for I am not aware that Waldeyer’s views upon this point have met with acceptance That author thinks that in chicks a thick germinal epithelium is indicative of female sex, whilst in males it is thin? Therefore, although at last these
1 Kierstock und Et, pp. 1383 and 135. 2 Tbid., p. 187.
glands differ so widely, yet at first they originate from a cell mass which is identical for the male or female; and which in its early stages betrays no evidence of its ultimate fate, whether destined to become an ovary or a testicle. Under these circumstances a suitable name has to be found for this indifferent rudiment, and it is usually called the sexual eminence. The sexual eminence of the rabbit’s embryo may be clearly seen during the thirteenth day of intrauterine life. Before describmg the manner of its appearance it is desirable, for reasons stated before, viz., the general untrustworthiness of time reckonings, to try to give an idea of the perfection of these embryos. Therefore, it may be said that the head and trunk together, although still curved upon each other, may be estimated to be about two centimetres long. The fore and hind limbs have incipient flexures; as yet they are deficient in digits, but:the latter are already foreshadowed by dark parallel lines in the somewhat spatulate ends of the limbs. Finally, the head and face are well formed, and the eye has a well-marked lens and choroid. The internal organs—the heart, lungs, liver, and intestines—are noticeable objects, but the permanent kidneys have not appeared. A transverse section through the middle of the abdomen of such a rabbit's embryo, that is to say, one of thirteen and a half days (fig. 37, p. 48), shows that the Wolffian bodies are large and elaborate organs. The enlargement is in a great measure due to an increase in the growth of the tubules, which, besides having a larger calibre, are more tortuous; moreover, it is obvious that the gland has larger glomeruli and is more vascular. The length of the Wolffian body is still very great compared with that of the embryo. It reaches from the diaphragm, which by this time has almost completed its development, nearly as far as the hind end of the peritoneal sac; in fact, it stretches nearly the whole length of the back of the abdominal cavity. In the specimen from which the drawing was made (fig. 37, p. 48) it happens that the genital eminence is already prominent, and consists of a collection of cells which are heaped up towards the front and inner side of the urogenital ridge, and very near the place where the latter abuts upon the base of the mesentery. At this time the bulk of the urogenital ridge consists of the Wolffian body and its various constituents. The relation of the genital eminence to the urogenital ridge may be illustrated by saying that, if the length of the ridge be divided into thirds, the genital mass would occupy rather more than the middle third! This is only an approximate estimate, because the eminence tapers at either end, and therefore it is hard to determine its exact limits.”
Fig. 37. — Wolffian body and sexual eminence of rabbit, 184 days. W.D., Wolffian duct; C.V., cardiac vein; Mes., mesentery; 4.0., aorta; G.M., genital mass.
The histology of the genital eminence in its earliest stages is of great interest and importance. In order to see the appearances which are described below, sections of extreme thinness are essential, and a high power, such as Zeiss, yyth oil immersion, should be used. If the section should happen to be at all thick, or the power low, the genital eminence looks like a homogeneous mass of cells. However, it consists of two sorts of
1 These remarks are also applicable to rats, corresponding in their development to thirteen days’ rabbits.
2 Foster and Balfour, Joc. cit., p. 221, say that at its first commencement in the chick the genital eminence extends the whole length of the Wolffian body and genital ridge, but subsequently is restricted to its anterior part. See also Waldeyer, p. 186, who makes a similar statement. a
elements, viz., of a stroma of large branched anastomosing cells, and of unbranched cells (fig. 26), contained in the meshes of the stroma. The relative proportions of branched and of unbranched elements is not the same throughout. Where: the eminence abuts upon the Wolffian body the network of branched cells predominates, and is very easy to see. It is continuous with the stroma of the Wolffian body, and the description which has been given to the latter applies to it in nearly every particular. The protoplasm of the branched cells is here and there collected into masses of some size, and where this happens large granular oval nuclei, which have one or more nucleoli, are usually seen (fig. 26). As the cells of the stroma approach the peritoneal surface of the genital eminence they, and their nuclei, become a little smaller, and there is a corresponding diminution in the size of their meshes. At the same time the stroma cells stain more deeply, and their nuclei are irregular in outline. In this and other specimens (fig. 32) some of the processes of the stroma are prolonged between the cells of the germinal epithelium as far as its peritoneal surface. As the genital eminence nears the Wolffian body its stroma becomes more palpable, but near the germinal epithelium it is partially obscured by a number of unbranched cell elements, whose nature is to be determined by an examination of the germinal epithelium. It is convenient todo this by simply tracing the lining epithelium of the abdominal cavity over the genital eminence (fig. 26). It has been said before that the peritoneal epithelium, at the thirteenth day, consists of a single layer of more or less cubical epithelial cells. Supposing that we look at this investment as it reaches the edge of the genital eminence, it may be seen that the individual cells have undergone considerable alteration. First of all, their size is no longer uniform, some being large and oval, others columnar, and not a few quite small and insignificant. So far as size is concerned, a very simple explanation is at hand, for a very active process of multiplication by fission is going on, and the smallest cells are simply those which have just been formed (fig. 26). But, returning again to the margin of the genital eminence and tracing the peritoneal epithelium over it,a marked alteration
in the disposition of the epithelium is to be observed. Instead of being arranged in an uniform layer their depth varies, and their deep surface has an irregularly festooned appearance. This appearance is caused by some of the cells of the germinal epithelium invading the stroma. These cells are recognisable because they stain more deeply than the larger oval cells which belong to the stroma, and because they have no protoplasmic branches. Whether the meshes of the stroma contain any other unbranched cells except these is hard to decide, but, after a great deal of study, I think that if thin sections are examined this question will be answered in the negative. It is exceedingly hard to give an adequate idea of this tissue either by description or by delineation, and although I think it is possible, even from early stages, to recognise the germinal cells, yet it is to be feared that only a very inadequate impression of their peculiarities has been conveyed. _
It is obvious that the preceding account does not apply to the very earliest beginning of the genital eminence. But before attempting that topic, a few spindle-shaped cells near the base of the genital eminence (fig. 37, p. 48) may be mentioned. They merely bound blood-vessels which, even at the thirteenth day, have entered the base of the eminence; and they belong to the stroma.
Further knowledge of the genital eminence may be gained from younger embryos, and is confirmatory of the preceding. However, this part of the subject is so important that perhaps it may be well to introduce it here, more especially as by so doing the study of the human embryo is facilitated. In a rabbit’s embryo at the beginning of the thirteenth day, and in. which the limbs were merely short protrusions, the lining of the peritoneal sac consisted of a layer of cubical cells, each containing a nucleus. These cubical cells were continued over the urogenital ridge without exhibiting any alteration except towards its inner aspect. In this situation, the spot which the genital eminence afterwards occupies, the cells are slightly more columnar (fig. 27) and lie at least three cells deep.. Although the various structures, such as tubules and glomeruli, contained in this rabbit’s urogenital ridge are not so perfect as they are in the chick at the fourth day—the period at which Waldeyer depicts the germinal epithelium 1—yet it may be assumed that
1 Waldeyer, Hierstock und Ei, p. 120, assigns a much greater distribution to
the thickening of the epithelium seen towards the inner side of the urogenital ridge of this rabbit is the beginning of its germinal epithelium. The section from which the drawing (fig. 27) was made came from about the middle of the ridge, and it was only in this neighbourhood that the thickening was seen} With regard to the characters of the cells of the germinal epithelium, it is to be noted that they stain freely and that those next to the peritoneal sac are columnar, whilst the deeper ones are more or less oval and have a conspicuous nucleus.
The tissue upon which the rabbit’s germinal epithelium rests, and which, of course, belongs to the urogenital ridge, consists of a network of branched anastomosing cells, many of which possess a large nucleus and nucleolus. The relation of this tissue to the germinal epithelium is most important. Where the two structures are in contact the basement line of the epithelium is not apparent, more particularly where the epithelium is thickest; and the union is so close that the processes of some of the branched cells are prolonged between the cells of the germinal epithelium.
The conclusions which it seems reasonable to draw from this account of the genital eminence of the rabbit is that that structure from its commencement consists of—A, Stroma; B, Germinal Cells; C, Blood-vessels.
Since it is quite clear from what has gone before that the human embryo has a urogenital ridge and germinal epithelium almost the same as in the chick or rabbit, it seems reasonable to suppose that it might also possess a genital eminence, and that the latter would originate in the same way as in the animals that have just been mentioned. A human embryo twothirds of an inch long, and whose arms and legs were short and devoid of flexures, seems to place this question beyond the stage of hypothesis. A section through the middle of the urogenital ridge of this specimen shows that there is a distinct elevation towards its front and inner side, and not very far from the base of the mesentery. This elevation mainly consists of mesoblast, and it seems reasonable to assume that it represents an early the germinal epithelium of the chick than can be seen in rabbits, or, I think, in human embryos.
1 Compare Waldeyer, Joc, cit., pl. v. fig. 50.
stage of the genital eminence. The arrangement of the neighbouring epithelium bears out this assumption. Near the place where the Wolffian duct lies in the urogenital ridge (fig. 28) the peritoneal epithelium is nearly flat, but as it nears the eminence which has just been mentioned its cells become larger and more columnar, and have many of the characters of germinal epithelium. In addition, the depth of the epithelium over the convexity of the eminence is greater than anywhere else. This thickening is due to an actual increase in the thickness of the germinal epithelium, and, besides, a number of its cells are mingled with those of the underlying mesoblast. These deeper cells are somewhat irregularly disposed, and indistinguishable from those which cover the surface. Making every allowance for the nature of the material which has afforded the foregoing information, I think that it would not be rash to conclude that the human embryo has a genital eminence almost identical in character and origin with that of the rabbit. Before taking leave of the human genital eminence a word may be spoken about the mesoblast which helps to form it. This tissue consists of quantities of small mesoblastic cells not much larger than lymph corpuscles. These elements are of various shapes—round, oblong, or spindle-shaped, and each possesses a nucleus. Whether any of them are branched at this early stage is hard to tell, because they are all so closely crowded together, much denser than in rabbits.
This point having been arrived at, the next question refers to certain peculiarities which are attributed to the cells of the germinal epithelium. Perhaps the point at issue may be made clearer by, the following quotation :!—
“This ‘sexual eminence’ is present in the early stages of both sexes. In both the epithelium consists of several layers of short cylindrical cells, a few of which are conspicuous on account of their size and their possessing a highly refractive oval nucleus of considerable bulk; in both the underlying thickened mesoblast consists—as indeed at this epoch it does generally in all parts of the body—of spindleshaped cells. The larger conspicuous cells of the epithelium, which appear to have quite a common origin with their fellow cells, and to arise from them by direct differentiation, and which are seen at the first in male as well as in female embryos, are primordial ova or primitive germinal cells. Thus in quite early stages it is impossible to detect the one sex from the other.”
1 Foster and Balfour, 2nd edit., p. 221.
Assuming that, so far as the chick is concerned, these observations are correct, we will now endeavour to see whether they can be applied to either the rabbit’s or human embryo.
After the description which has been given of the rabbit's germinal epithelfum it is unnecessary to institute tedious comparisons. Although that animal does not possess primitive germinal cells which conform exactly to the description of those of the chick, nevertheless the deeper ovoid cells of its germinal epithelium may be their representatives. It is true that it can hardly be said that “they are conspicuous on account of their size,” or that they “ possess a highly refractive nucleus of considerable bulk”; but that some of the deeper cells of the rabbit’s germinal epithelium betray a distinct resemblance to the primordial ova of the chick, and that they appear to become an integral part of the genital eminence cannot be denied. Moreover, speaking more particularly of ova, when it is considered how, at maturity, the avian ovum differs from that of the mammal, ought we to wonder that their early stages are not quite the same. It seems qs though the ovum of the bird began to assume its peculiar characters, especially largeness, from its very beginning; but that in the rabbit and human embryo the germinal cells hardly acquire such a definite individuality.
The quotation raises another question, viz., the characters of the mesoblastic tissue which helps to form the genital eminence. It is said that in chicks at the fourth day of incubation the mesoblast which underlies the germinal epithelium consists of spindle-shaped: cells; but Waldeyer, also speaking of chicks at the fourteenth day of incubation, says that the tissue in question consists of ordinary small round or flattened cells joined to one another by branches, and that they are the same as the connective-tissue cells which at this period are found throughout the embryo. In addition, he mentions that a slight augmentation of this tissue causes the elevation which constitutes the genital eminence, and in his figure a colony of nucleated cells is indicated in this position. The whole of this description, the correctness of which I have assured myself, might be applied to the rabbit’s embryo, with the exception that in them there is hardly any increase in the density of the stroma which underlies the germinal epithelium. It is to be understood that this statement applies to very thin and highly magnified sections. In human embryos which show the earliest stages of the genital eminence, the tissue subjacent to the germinal epithelium is rich in cells of various shapes and sizes, but, owing perhaps to the nature of the material, the network of branched anastomosing cells is not perceptible ; however, it is very obvious in the latter stages of the development of the human testicle.
1 Zoe. cit., p. 136.
It has been deemed expedient to describe the genital eminence of the rabbit at some length, because, although its histogenesis is most probably the same in the human embryo, yet, as I have often said, the material they afford is seldom good enough to serve as the basis for imdependent conclusions. Nevertheless, it is easy to understand that, although this be the case, human embryos may furnish a great deal of information which is reliable when supported with evidence derived from examination of other mammals.
When once the genital eminence has become established, its growth proceeds apace. By the seventh week, in human embryos, it is almost equal in bulk to the Wolffian body, and by the tenth week is larger than that structure ; a superiority which it ever afterwards maintains. But before passing to these later stages it. is desirable to mention some of the steps by which they are reached. So far the Wolffian body, both in rabbits and in human embryos, has been the main representative of the excretory system. However, the definite establishment of the genital mass determines an important alteration.
Before this event the Wolffian body throughout its whole extent seems qualified to perform the duties of a great excretory organ. But a time has arrived when the genital mass originates and grows in its proximity, and henceforth the Wolffian body, instead of fulfilling its manifest destiny—to function as an excretory organ—becomes a mere appendage of the newly arisen sexual gland, and eventually is the epididymis. No immediate alteration in the appearance of the Wolffian body denotes this change in its destiny, but nevertheless the organism has to make provision for the performance of the functions for which the Wolffian body has presumably become incompetent. Under these circumstances, the permanent kidneys begin to originate. In rabbit’s embryo at about the middle of the thirteenth day of intrauterine life, and in which the genital eminence is comparatively small, and whose Wolffian body is still large, the ureter is the only part of the permanent excretory apparatus which has appeared. This canal springs from quite the hinder end of the Wolffian duct, and running towards the head and behind the posterior part of the Wolffian body, ultimately terminates in the kidney. The latter organ -is, as far as I have been able to ascertain from the examination of numerous human embryos and many rabbits, even from its earliest beginning, quite separate and distinct from the Wolffian body (fig. 29). When the kidneys appear the limits of the Wolffian body are very definite, and there is no admixture of its canals with those of the kidney. As for pretending to distinguish the canals of the one organ from those of the other, it would, in my opinion, be exceedingly difficult, or perhaps impossible. If these points are conceded it would seem superfluous to invoke the existence of misplaced Wolffian tubules for the purpose of explaining congenital cystic conditions of the kidneys. Some malformation of the kidney tubules themselves, or of the glomeruli, would afford an equally plausible explanation, and would not necessitate a demonstration of the passage of Wolffian tubules into places where they do not normally exist.
The permanent kidneys seem to me to originate in the rabbit and rat in the manner described by Kolliker.? Sections through rabbits at the commencement of the fourteenth day, in my opinion, confirm the statements of that author. After the Wolffian duct has received the whole of the Wolffian tubules it ruts a little distance towards the tail end, and terminates in the urogenital sinus. Just before its ending the Wolffian duct receives a canal which closely resembles it in appearance and size. This canal extends forward towards the head, pursuing a course parallel to, but behind, the Wolffian duct, and when it
1J. Bland Sutton, ‘‘ Erasmus Wilson Lectures on Evolution in Pathology,” Lancet, 1887, voli. p. 355. |
Kolliker, loc, cit., p. 946, figs. 579 and 580.
has arrived behind (7.¢., dorsal to) the hinder extremity of the Wolffian body terminates in two or three cecal prolongations (fig. 29). These latter represent the commencement of the kidney, and they are lined with a single layer of columnar epithelium. This lining differs from that of the ureter, with which it is continuous, merely in the length of its cells: instead of being short columnar like those of the ureter, they are exceedingly long. Although these remarks are founded upon observations made upon rabbits, I have also found that they are applicable to the rat. Before leaving the subject an aggregation of mesoblastic cells (kidney blastema) which surrounds the rudimentary kidney tubules calls for remark. It is present both in rabbits and rats, and gives origin to the parenchyma of the organ. It is not proposed to pursue this question any further at present, but perhaps enough has been said to establish the independence of the permanent kidneys and Wolffian bodies. By the end of the fourteenth day the original prolongations from the ureter have been reinforced by many others, and the permanent kidneys are well established. A transverse section through an embryo rabbit, of the fourteenth day after impregnation, shows the relation of the comparatively well-developed kidney to the hinder part of the Wolffian body and to the genital mass (fig. 30). The genital mass may be seen lying to the front and inner side of the Wolffian body, and immediately behind the latter is the rudimentary kidney. Longitudinal sections show that by this. time (fourteenth day) there is in rabbits a close correspondence between the anteroposterior limits of the genital mass and those of the kidney, the former, of course, lying in front of the Wolffian body, the latter occupying a.corresponding position behind it. Moreover, by this time the Wolffian body has become slightly curved, the concavity of bend being towards the middle line, and embracing the genital mass. For this reason it is impossible in a single longitudinal sagittal section to demonstrate all the foregoing points; a series must be examined. If, for a moment, attention be given to the section of the fourteen-day embryo (fig. 30), the elaborate structure of the Wolffian body is evident; tubules and glomeruli may be seen in great profusion. The sexual gland adheres to its inner side by a broad base, and its substance is DEVELOPMENT AND TRANSITION OF TESTIS. 57
continuous with that of the matrix of the Wolffian body. Under low powers the genital mass looks not unlike ordinary lymphoid tissue, but highly magnified it consists of a very delicate stroma of branched anastomosing cells with a great abundance of round, unbranched, nucleated elements entangled in the meshes (fig. 32). <A glance at the kidney is sufficient to prove its rudimentary nature, for it consists of a collection of nucleated cells, contained in a meshwork of branched, nucleated, anastomosing cells, penetrated by a few tubules, offshoots from the ureter. The entire independence of the kidney substance from that of the Wolffian body is very obvious.
Human Genital Mass
In the rabbit at the fourteenth day the Wolffian body still reaches from the diaphragm to the pelvis, and, roughly speaking, the middle third of its posterior surface is in contact with, but distinct from, the developing kidney; further, it is apparent that the side of the Wolffian body away from the kidney is in relation with the genital gland (fig. 31)... The next step is to see how far these observations are applicable to the human embryo.
In a human embryo at about the fifth week of intrauterine life the genital mass, or sexual gland, was a prominent object (fig. 32). It lay rather nearer the outer side of the Wolffian body than is the case in the rabbit, and the section which passes through its midst also divides the lower part of the kidney. As far as I can judge, the Wolffian body of this embryo is normal so far as its histology is concerned, but in a little while a most interesting abnormality of its hinder end will be referred to. However, our present object is to ascertain the relation of the genital gland and Wolffian body to the kidney. It may be said at once that these relations are the same as those which have just been noted in the fourteen-days’ rabbit, the only difference being that the sexual organs are not quite so much in front of the kidney as they are in that animal, but more to the outer side. The sexual gland also betrays in its structure another divergence. Even when examined under low powers it
This is more apparent in sections nearer the head than that drawn in Plate II., fig. 30.
is clear that many of the cells which compose it are arranged in columns which radiate from the centre towards the periphery. This feature was not visible in the rabbit, but in this and other human embryos it is very obvious, and may indicate, I think, the commencement of the seminal tubules! Some of the sections obtained from this specimen show that a layer of cubical epithelial cells covers the surface of the genital mass, but, with the exception of the point which has just been mentioned, and which relates to the disposition of the cell elements, the histology is not quite so definite as in the rabbit. The material is hardly good enough to justify very positive statements, but it is quite clear the genital mass consists of two sorts of cell elements; the most conspicuous are those which have been said to have a tendency to arrange themselves in columns, and these are fairly large, deeply stained, unbranched, nucleated cells; the others are situated between and amongst the latter; they are nucleated, but do not stain so well, and are irregular in outline, perhaps branched. It is important to notice that, although the Wolffian tubules are very close to the genital mass, yet they do not penetrate into its substance.
Following onwards the natural sequence of events, two changes which take place at the same time would naturally call for notice. One of these changes is histological, and has to do with the development of the seminal tubes and those of the epididymis ; the other 1s anatomical, and produces the mesentery of the Wolffian body and testis, a structure by means of which those organs become more free and mobile in the abdominal cavity.
Before raising these questions it seems appropriate to mention the abnormality which, as was said before, affected the hinder part of theWolffian body and genital mass of the embryo which has just been described.
Fusion of Wolffian Bodies—Synorchis
This is the earliest abnormality which has been met with in these researches, and the embryo in which it was found was about two-thirds of an inch long, and its arms and legs were already beginning to exhibit incipient flexures. In all respects this specimen seemed to be normal and in good condition, but, at its pelvic end, the Wolffian bodies of opposite sides were fused for a few sections. This part of the organ, viewed in section (fig. 38, p. 59), was exactly like a horse-shoe kidney. The upper part of the Wolffian body, as I have said before, seemed quite ordinary, and a normal genital mass grew in relation with it (fig. 31).
- 1 The expression “tubules ” is, of course, incorrect, because these structures are solid columns of cells and possess no lumen.
Fig, 38. — Human embryo sixth to seventh week. The Wolffian bodies are blended towards their hinder ends.
It is interesting to speculate upon the condition which might have been found in this case had the embryo ever grown to maturity. Without doubt the testes must have been united to one another. Sweh-occurrences are not unknown, but must be infinitely rare, © 0 231- Although systematic writers are accustomed to speak of union of the testis, I am not aware of more than one really authentic instance. This rare case is narrated by Geoffroy Saint Hilaire,! who was indebted for the details to Breton and Charvet, both of whom seem to have been very competent observers. Perhaps I may quote Mr Curling’s? translation of the paragraph, because he has alluded to the circumstance and adds that he believes the case to be unique. “An infant was born at Vizille in 1812: several physicians consulted respecting the child’s sex and were of different opinions; they decided, however, to inscribe it in the registers as a girl. It died at the age of eighteen months, and was dissected by Breton, who recognised a complete hypospadias. The scrotum was bifid and empty; and the two suprarenal capsules, as well as the two kidneys and the two testicles, were joined together in the middle line. The spermatic arteries and veins, vesiculze seminales and vasa deferentia exhibited nothing remarkable, each half of the double testicle receiving its particular vessels,” Curling proceeds to mention a case of synorchis which Sedillot found whilst examining a recruit, but there is no evidence beyond the mere surmise. Saint Hilaire also alludes in doubtful terms to another case. It is evident that the account which has just been quoted is wanting in many important particulars. For instance, it is not said whether the bodies of the testes were fused or their epididymes, or what relation the abnormal gland had to the other abdominal contents. Under ordinary conditions the mesentery separates the testes, but in such circumstances as are being discussed, it must have become modified. In the case depicted (fig. 38, p. 59) it is clear that the Wolffian bodies fuse just behind the posterior end of the alimentary canal. Curiously enough, in this embryo the kidneys: themselves blended for a little way at their hinder extremities, but none of the other paired organs were united.
- 1 Geoffroy Saint Hilaire, Histoire des Anomalies, 1832, t. i. p. 542. The doubtful case is by Acrell, in the Schwed. Abhandl., t. xii. p. 19.
- Curling, On Diseases of the Testis, 4th edit., 1878, p. 6.
Mesorchium and Mesovarium
As far as we have at present traced the development of the genital system, either in rabbits or in human embryos, the determination of the sex, in spite of that which Egli! and Waldeyer have said, seems with our present knowledge an impossibility. Whether the radiating arrangement of the unbranched cells of the genital mass, which is seen in some human embryos, may be an indication of the male sex, is of course a matter of doubt, and incapable of direct proof. However, the events which now occur speedily set all doubts at rest. Whether the embryo is destined
1 Egli, Th., Beitrage zur Anat. und Entwicklungsgeschichte der Geschlechtsorgane, Ziirich, 1876.
to belong to the male or female sex has no influence upon the alterations which take place in the relations of the Wolffian body to the dorsal wall of the abdomen, or in the alterations which take place in the relations of the genital mass to the Wolffian body. Important modifications take place in these particulars, either in males or females, and since they are far advanced long before the histological details of the sexual organs are perfected, I will consider them first.
Fig. 39. — Human embryo (seventh week) ; section towards middle line. A.W., portion of Wolffian body which atrophies; G.M., genital mass; W.T., Wolffian tubules; W.D., Wolffian duct; M. D., Mullerian duct.
The process by which the genital mass is constricted from the Wolffian body, and by which the latter is freed from the dorsal wall of the abdomen, takes place almost directly after the genital mass hasappeared. A glanceat fig. 37, p. 48, which was made from a transverse section through the genital eminence of a rabbit during the thirteenth day of intrauterine life, shows a faint constriction at the junction of the genital mass with the Wolffian body ; and, moreover, the latter, in proportion to its size, possesses a narrower dorsal attachment. Although these particulars are not so obvious in fig. 31, which was made from a transverse section through a human embryo of about the fifth week, yet indications of their presence are not wanting. However, on the fourteenth day the Wolffian body of the rabbit possesses a broad but distinct mesentery of its own (fig. 30), and the same statement holds good for human embryos which have reached somewhere near the sixth week of intrauterine life. In transverse sections made through human embryos at that period the Wolffian body has a well-marked mesentery, which is attached to the dorsal wall of the abdomen just external to the kidney, and in addition there is an obvious constriction between the Wolffian body and genital mass. Both in human embryos and in rabbits the processes which have commenced in this manner continue to progress, until at last the Wolffian body has a distinct mesentery, which becomes the mesorchium or mesovarium, and the genital mass is merely fastened to the Wolffian body by a narrow neck (fig. 39, p. 61). The changes by which a mesentery 1s formed for the Wolffian body and genital mass occur in exactly the same way in either the male or female sex, but whilst they are taking place the histology of the genital mass has undergone great alterations, and moreover the Wolffian body has been profoundly modified.
Development of Tubule Seminifere
Perhaps it will make that which follows clearer if I begin by pointing out the order in which the process of development will be followed. It is quite unnecessary to premise that the genital mass, although at first seemingly indifferent and suitable for conversion into either ovary or testicle, becomes transformed either into a highly complicated tubular organ or into a cell-laden mass. It is not proposed in this place to discuss the conversion of the genital mass Into an ovary, but to endeavour to show how it gives origin to the connective tissue and tubules of the testicle, and how the latter acquire their needful efferent channels. Although human embryos are obtainable suitable for showing the larger details, nevertheless they are rarely good enough to demonstrate the more minute histological changes. It is not necessary on this account to repudiate them altogether, but it makes it desirable to check all conclusions drawn from them by the examination of more reliable material. Under these circumstances the histology of the developing testicle of the rabbit will, first of all, be mentioned, and afterwards the development of the human testicle will be illustrated. But, as we proceed, it will be found that rabbits need only be used in the earliest stages, and that for the final ones human embryos of a satisfactory character are at hand.
We have already described the formation of the genital eminence of the rabbit in its earliest stages. It is unnecessary to recapitulate either its mode of origin or its relation to the Wolffian body. It will suffice to recommence the consideration of its histological structure by referring to the appearance which it presents during the first half of the thirteenth day. Since these have been described in detail, they only call for brief allusion. It may be remembered that from its earliest commencement the genital eminence consisted of a network of branched anastomosing cells, which was continuous with the stroma of the Wolffian body. The meshes of this network contained numerous nucleated unbranched cells, which were in continuity with, and the same as, the germinal epithelium (fig. 26).
The part of this account around which a great deal of controversy turns is the exact relation of the cells of the germinal epithelium to the rest of the genital eminence. Kolliker! states his belief that the germinal epithelium only gives origin to the ova and to Muller’s duct; but, at the same time, he says that many authors think that it has a much greater réle to play. The preparations from which the preceding account was written were exceedingly successful, and, in my opinion, showed that the germinal cells penetrated almost half-way towards the base of the genital mass. The embryos had. been stained in picrocarmine, by which the germinal cells were deeply coloured— much more deeply than those of the stroma, Janosik gives a description very similar to that which I have endeavoured to set forth ; but that author does not, in my opinion, lay sufficient stress upon the stroma of the genital mass. He has compiled an excellent epitome of the opinions held by many recent authors.
- 1 Kolliker Pp, 959. 2 P, 147 et seq.
Although at the beginning of the thirteenth day the germinal epithelium of the rabbit has those appearances, nevertheless at the fourteenth day it still looks almost uniform in structure. Transverse sections made through the genital eminence during the latter period show that its surface is covered with a layer of small cubical cells, and that its bulk consists of a network of branched anastomosing cells, with a number of unbranched nucleated cells in the meshes (fig. 32). There is no feature about the histological appearance of these unbranched elements to positively identify them with the germinal cells; we can only assume, from the preceding observations, that they have been derived from that source. Whilst in this indifferent stage the genital mass, when looked at with a low power, is very like lymphoid tissue. Even high powers do not.dissipate this impression, more particularly as regards the stroma; but the cells in the meshes do not at all resemble lymph cells; they are larger, and have a more clearly defined nucleus, and a larger quantity of protoplasm.
Although human embryos are seldom good enough to demonstrate such minute histology as that which has been described, nevertheless the genital mass of a human embryo (fig. 39, p. 61), of about the seventh week, was almost the same as that of the rabbit at the beginning of the fourteenth or end of the thirteenth day. Both as regards stroma and unbranched cells the similarity is quite clear.
Remembering that the genital mass consists of a network of branched anastomosing cells, in the meshes of which are numbers of round nucleated elements, we may now proceed to observe how the seminal tubules originate in this tissue. The commencement of the process may be seen in the rabbit’s embryo during the fourteenth day. About this time an alteration may be noticed in the tissue which underlies the surface layer of cubical epithelium. This change consists in a more or less complete disappearance of unbranched cells from the stroma in this situation, and in the stroma itself forming a narrow pheral zone, which differs from the central part in the smaller and more elongated character of its meshes (fig. 32). This layer, which represents the commencement of the tunica albuginea testis, is arranged with the long axis of its meshes parallel to the surface epithelium. Towards the centre of the sexual gland other alterations may be seen in the stroma, for its meshes but the arrangement of the other constituents, more particularly of the unbranched cells, is very interesting. Ifthe microscopical examination is begun with a low power, such as a third of an inch, it is easy to see a rudimentary tunica albuginea beneath the surface, and this is developed, as in the rabbit, by the meshes of the stroma becoming parallel to the surface epithelium, and by the disappearance of unbranched cells from its meshes.
Fig. 40. - Relation of testis T. and Wolffian body to kidney K., ilium Il., and to the front wall of abdomen ; H., heart.
have in places become exceedingly large, so that aggregations of the unbranched cells are observable. That this betokens the beginning of the seminal tubules will, I think, be conceded after the testicle of a human embryo of about the tenth week has been described. Before entering upon these particulars it may be as well, for reasons which have frequently been stated, to give a brief account of that specimen (fig. 40). The length of a longitudinal section through the body and trunk was one inch and three-sixteenths, the limbs were well formed, and possessed, besides proper joints, well-marked fingers and toes. The testes and Wolffian bodies lay in contact with, but posterior to (ie,, below, in the erect posture), the kidneys; and as this is a point which will be discussed further on, we may now proceed to examine the histological structure of the testes.
At this stage of development the sexual gland has the general contour of the perfect organ and the Wolffian body has begun to have a likeness to the epididymis. The surface of the testicle is covered with a layer of cubical epithelium, and its interior is made of a stroma of large branched anastomosing cells and of numerous unbranched nucleated elements. The epithelial covering has no peculiarity, and may therefore be passed over;
Fig. 41. - Section through Testis at tenth week to show developing seminal tubules and stroma. Ep., epithelium ; T.A., tunica albuginea ; S., stroma; T.T., tubuli testis. x 250.
Throughout the rest of the gland the stroma, under low powers, has no peculiar feature. If now we pass on to the unbranched cells, or, as in future they may be called, spermatic cells, it will be found that, instead of being uniformly scattered throughout the testicular stroma, they have disposed themselves along certain paths. The irregular columns which have thus originated have an arborescent appearance, which indicates that they are the commencement of the seminal tubes (fig. 41, p. 66). As these rudimentary tubules approach the tunica albuginea they loop backwards again towards the centre of the testicle. Moreover, near the junction of the testicle with the Wolffian body, or, as in future it may be called, the isthmus testis, the converging tubules are jomed to one another by numbers of spermatic cells, which are irregularly arranged along the long axis of the testicle, and represent the rete testis (see also fig. 33). Placing aside, for the moment, the development of the efferent channels of these newly developed tubules, we may proceed to consider the more minute histological characters. For this purpose an amplification of about 250 diameters is enough, and what follows relates to the testicle of a human embryo at about the tenth week of intrauterine life seen with such a power (fig. 41, p. 66). So far as its general arrangement is concerned the stroma is the same as that which has been described already in the developing testicle of the rabbit. But it is to be noted that the strands which form the meshes of the stroma are a great deal thicker. | Moreover, the thickness of the strands of the stroma is not the same everywhere ; they are thinnest towards the periphery, but become thicker towards the isthmus testis. Near the tunica albuginea it is easy to see that any particular portion of the testicular stroma is made of branched anastomosing cells, which possess large, granular, oval nuclei and nucleoli; but as the strands of the stroma approach the isthmus it is clear that, although its individual cell elements are the same, yet their relations to one another have altered. The alteration is in the shape of the cells, which, mstead of being provided with long and tenuous branches, have either none at all, or, in their place, thick and short protrusions of their substance, and these are continuous with other cells. Owing to these modifications there are places near the isthmus testis and near the rete where the stroma is made of strands of cells which seem to possess no branches, and which, lying side by side, closely resemble endothelial plates. Where this is the case it would be easy to mistake the unbranched stroma cells for endothelial plates, but, even where the likeness is strongest, traces of a meshwork are here and there discoverable. These appearances have been particularly mentioned because of their importance when taken in relation with certain columns of cells which have been observed in hilum of the mature testicle. Dr Klein! describes and figures certain “interstitial epithelial cells” in the hilum of the mature testicle of the cat, and attributes them to the tubules of the Wolffian body, of some of which he considers them to be the remains. Judging from Dr Klein’s very beautiful figure, and from specimens of cats’ testicles, the structures in question look to me much more like the cells of the developing stroma, such as I have just described. This is not intended to imply that no tubules from the Wolffian body enter the hilum of the testicle (or ovary), and in that which follows evidence will be forthcoming upon this point.
Before taking leave of the stroma of this testicle, it is hardly necessary to do more than mention that it is continuous at the isthmus testis with the stroma of the Wolffian body. The latter has already been depicted and described (fig. 25), and calls for no further mention. It only differs from the stroma of the body of the testiclein not forming strands, and in an absence of collections of endothelial-looking stroma cells, such as have just been alluded to.
The next question that demands attention is the histology of the developing seminal tubules, and of the spermatic cells which compose them. If a clear idea has been conveyed of the rudimentary testicular stroma this should prove an easy task. The spermaticcells stain moredeeply than those of the stroma,and each one has a central nucleus and nucleolus. Their shape is round or oval, and they have no branches whatever. It has been said that the spermatic cells are arranged in irregular arborescent columns, and now, under high powers, it is seen that these columns lie in irregular spaces in the stroma (fig. 41, p. 66). These latter are not anything special, and merely look like enlargements of the meshes of the stroma; but the outline of their walls is more regular and definite, and the cells which form their boundaries are usually flat or spindle shaped (fig. 41, p. 66).
1 Klein, Atlas of Histology, p. 269 and 286, pl. xxxix. fig. 3.
The columns of spermatic cells which lie in these spaces have no particular arrangement, but their tendency seems to be to occupy the centre, and not to lie in contact with its walls. However, it is most interesting to observe that, whilst in this rudimentary state, the spermatic tubules are solid, and composed of small round or oval cells arranged without any particular order.
Owing to the kindness of Mr Hy. Butlin and Mr A. Bowlby I have had the opportunity of examining histological sections of sixteen malignant tumours of the testicle. It was impossible tv ignore the great likeness of their tissues to those of developing testis. A stroma of branched anastomosing cells was visible in portions of many of them, and their unbranched elements were practically indistinguishable from the unbranched spermatic elements which have just been described. In none of these malignant tumours could I discover, even after several careful examinations, any elements to which I myself should apply the term “epithelium.” On the contrary, specimens which would accord with the definition of a cancer seem to do so because their unbranched elements were collected into irregular columns, like developing seminal tubules! With regard to the existence of epithelium in tumours of the testicle the foregoing statement requires to be qualified to this extent, namely, that I have more than once seen in them tubules or loculi lined with a single layer of columnar epithelium. However, in those cases there was no real resemblance to any ordinary form of carcinoma, and the tumours usually contained cartilage and other mesoblastic elements.
If the order of development was strictly followed the Wolffian body would again claim attention. That organ has, whilst the body of the testicle has been developing, undergone great changes, and is in course of being converted into the epididymis. But to avoid leaping from one branch of the subject to another it is more convenient to carry the development of the body of the testicle a stage further, and then return to the Wolffian body.
1 B. Rindfleish, Lehrbuch der Patholog. Gewebelehre, Leipzig, 1886, p. 579, quotes from Birch-Hirschfeld, “that the cells, as in cancers of kidney, liver, breast, and testicles, come from the epithelium of the gland canals.
We have just seen that the seminal tubules of the human embryo, and also the rete testis, are laid down as early as the ninth or tenth week of intrauterine life, so that it only remains to trace their future modifications.
The appearance of the human testicle at the third month has been figured in the accompanying sketch (fig. 33). The seminal tubules are more numerous and thicker, and the rete testis is very much better marked than in the younger embryo. This is due to an increase in the numbers and in the size of the spermatic cells. Both the seminal tubules and the rete testis are solid columns of unbranched, deeply staining, nucleated cells. Evidently the term “tubule” ought not to be applied to these structures until they have acquired a lumen. At the sixth month of intrauterine life the arrangement of the spermatic cells has not altered, but the seminal tubules are larger, and have begun to be exceedingly tortuous. I have no exact information as to when the centre of the seminal columns begins to clear, but in the testicle of a young goat, six months old, there was a very slight indication of a clearing towards the axis of the column.
The phases through which the connective-tissue stroma of the developing testicle passes are comparatively simple. Although up to the tenth week the stroma of the human testicle consists of branched elements, yet by the twelfth week the cells are in places elongated and beginning to be spindle shaped (fig. 33) ; by the fifth month they have advanced a long way towards being fibrous tissue, and, of course, this is its ultimate destiny (fig. 35). As for the interstitial cells, which may be seen in the stroma of well-prepared sections of adult testicle, it has been said that they are formed from remains of the Wolffian body. The time has now arrived at which we may conveniently endeavour to ascertain the relation of the tubules of the Wolffian body to those of the testicle; and as this important branch of the subject is followed, ight will be thrown upon this important and interesting question.
As suitable material is at hand, I propose to confine the rest of this description to human embryos. But, before entering upon particulars, it is desirable to endeavour to convey an idea of the general appearance and relations of the genital mass at the time when the changes which are about to be mentioned begin. In a human embryo five-eighths of an inch long, and at about the seventh week of intrauterine life, the Wolffian body and genital mass lay near the lower end of the kidney, and just overlapped that organ. The genital mass was in the indifferent stage, and it is impossible to be sure of its ultimate fate; it is attached to the middle third Wolffian body by a narrow isthmus (fig. 39,p.61). The Wolffian bodies themselves are not by any means so parallel to one another as when first developed, and lie obliquely, with their lower ends converging. There is no difficulty in observing that its structure has undergone great alterations. If we begin with a section near the middle line, and therefore dividing its lower part, it is evident that the foremost glomeruli, although larger, are faintly stained, and their tissues granular,—appearances which indicate that they have begun to degenerate and atrophy. The tubules, on the other hand (fig. 39, p. 61), are exceedingly perfect; their lumens are capacious, and their lining membrane of short columnar epithelium is very distinct (see also figs. 24 and 25). Turning now to a section which divides the upper and outer part of the Wolffian body, quite a different sort of tubule comes into view (fig. 34). These may be said to begin in a collecting tube, which is a continuation forwards of the Wolffian duct. I have purposely refrained from calling this the Wolffian duct, to mark that its characters are decidedly dissimilar, being smaller, and having hardly any lumen. The tubules, which extend from the collecting tube into the hilum of the genital mass, are still more remarkable. In this and other specimens about twenty tubules leave the collecting tube at right angles, and extend into the hilum of the genital mass. At their beginnings these canals have hardly any lumen, but they expand as they run onwards, and gradually acquire one. Their epithelium is peculiar in that it stains exceedingly dark, and in being smaller and more cubical than that of ordinary Wolffian tubules! (fig. 34). When we consider the course and the relation of these peculiar tubules to the genital mass, it does not seem unreasonable to suspect that they are the commencement of the tubuli efferentia. Waldeyer has given semi-diagrammatic representations of these tubules;! the human embryo which he used was 9 cm. long, and therefore much older than that which I have been describing. Waldeyer divides the Wolffian body into two parts: a sexual, consisting of these tubuli efferentia; and a urinary, consisting of the more capacious tubules and glomeruli, At present we are not concerned with the female type, but 1t may not be out of place to note in it the destination of the genital mass, and of the sexual and urinary parts of the Wolffian body; the genital mass becomes converted into the ovary; the sexual part of the Wolffian body remains as the structure which Waldeyer calls the “Epoophoron”; and the urinary part also persists, and is called by the same author the “Paroophoron.” The terminology of these remains is exceedingly confused. Authors have not always drawn a clear distinction between the sexual and urinary portions of the Wolffian body. The former, as we have seen, are smaller, straighter, and less canalised than the others, and have apparently no glomerull ; moreover, they penetrate into the genital mass, The urinary tubules are larger, have a wider lumen, and end in glomeruli, and do not penetrate the genital mass (fig. 39, p. 61). In order to avoid ambiguity, a provisional list of the various names which are commonly applied to these various structures is appended, and has been compiled from the books of Henle, Kdlliker, Quain, Waldeyer, &c.
- 1 The sexual canals of the human Wolffian body require to be studied in suitable transverse sections, and this would, I am sure, throw light upon their origin.
Provisional List of Names
|In Female||In Male|
|Genital mass becomes:||Ovary||Testicle|
|Wolffian body becomes:|
|A, Sexual part||Epoophoron of Waldeyer
Parovarum of Kobelt
Organ of Rosenmuller
|Vasa efferentia or Coni vasculosi|
|B. Urinary part||Paroophoron of Waldeyer.||A. Paradidymis of Waldeyer, or Organ of Giraldés,
B. Vasa aberrantia.
1 Kierstock und Ei, p. 142, also plate vi. figs. 60 and 61.
Before I endeavour to trace the process by which, in the male, the sexual tubules of the Wolffian body become vasa efferentia, a peculiarity which they betray during the indifferent stage may be noticed (fig. 34). Where these tubules open into the collecting tube they are small, and have hardly any lumen, but as they run towards the hilum of the ovary they expand, and have at last a considerable dilatation (fig. 40).
The meaning of this seems obscure, and, as far as I am aware, has not been noticed before. However, Waldeyer made his semi-diagrammatic figures from older human embryos, and I have reason to think that in them the dilatation is not discernable.
The sex of the embryo from which the foregoing observations were made could not be distinguished. Its genital mass was in the indifferent stage, and had neither tunica albuginea nor the rudiments of seminal tubules, and therefore it affords no clear evidence of the way in which a communication is effected between the tubules of the Wolffian body and those of the testicle. The human embryo of about the tenth week may carry us a step further (fig. 40, p. 65). This embryo has already been mentioned, and the development of the body of its testicles has been traced up to the point at which it consisted of solid arborescent columns of cells converging to a rete testis all imbedded in a stroma of branched anastomosing cells, and surrounded, except at the isthmus, by a tunica albuginea. The Wolffian body of the embryo, like the last, consisted of two portions distinguished by the dissimilarity of their tubules; these parts being, of course, those which have been called the sexual and the urinary. The urinary part of the Wolffian body, if we may judge from the perfection of its structure (fig. 25), is at the height of its development, and in size far exceeds the sexual part. This latter contains the curious tubules which have just been described and identified with the vasa efferentia. They are a quarter the size of the urimary tubules, and their epithelium stains darkly; they run nearly at right angles from the collecting tube, and extend into the hilum of the testicle, where they are slightly dilated, and have alumen. With regard to this last point it is interesting to note that it is exceedingly hard to say whether either the foremost part of the collecting tube, or the portions of the tubules (tubuli efferentia) nearest to them have a real lumen. However, in the hilum of the testicle the latter are canalised, and some of them contain a structureless substance, which stains faintly, and is doubtless some form of secretion. This embryo is, without question, of the male sex, and it shows, at least, that the sexual tubules reach the body of the testicle.
But, before it is possible to form any conception of the way in which the sexual tubules of the Wolffian body become continuous with the rete testis, perhaps it may be desirable to call to mind the anatomical arrangements at this particular moment. Both in the ten weeks’ embryo, and in one of twelve weeks (fig. 23), there 1s, at the isthmus of the testicle, no line of demarcation whatever between the parenchyma of the testicle and that of the Wolffian body. The aggregation of spermatic cells which constitutes the rete testis is in the stroma, and has no distinct limits (fig. 23). Moreover, the tubules of the sexual part of the Wolffian body or vasa efferentia extend into the hilum of the testis, and gradually lose their identity, owing to their cells having become disseminated in the meshes of the stroma. But those meshes are full of rounded unbranched seminal cells, so that there is a continuity of cell elements between the rete testis and vasa efferentia. As cell arrangement proceeds in the body of the testicle, these intermediate cells form the last link in the chain which unites the sexual tubules of the Wolffian body to the rete testis. The actual arrangement of these indifferently disposed intermediate elements does not begin in the human embryo until about the sixth month of intrauterine life. The accompanying drawing has been made from the testicle of a human embryo at about the eighth month of intrauterine life (fig. 35), and although it does not demonstrate an absolute physical continuity of cell elements between tubules of epididymis and those of the testicular lobules, yet, in my opinion, such an union does exist. The elements are arranged in irregular and crooked strings, so that no single section could give adequate evidence upon this point.
This account of the process by which an egress is provided for the seminiferous tubes is, allowing for differences in the mode of expression, very like that which Janosik describes for the rabbit and cat. However, the examination of testicles of various animals—dog, cat, goat, and rabbit inclines me to believe that the process is not the same in every type, but that the tubules of the Wolffian body may participate in different animals to a varying extent in forming the rete testis. If this surmise be correct, it would tend to explain the various and contradictory accounts which may be read in the voluminous literature of the subject. Under these circumstances, it has been deemed advisable to adhere to one type, and human embryos seem as suitable as any others, and have, therefore, been used. It is not proposed to follow the histological differentiation of the tubules of the testicle and epididymis beyond the process of establishment. But before leaving the subject, a word may be spoken upon the fate of the glomeruli of the urinary portion of the Wolffian body. These have been seen at the height of their perfection in male human embryos of the tenth week (fig. 25). At the twelfth week it was still quite easy to ascertain their persistence; but in the male none could be found at the sixth month, nor at the eighth month.
But, in a specimen of the ovary and broad ligament of a child eight months old, lent to me by Dr Walter Griffith, there were structures near the hilum of the ovary which had the usual characters of glomeruli, except that Wolffian tubules were not traced to them.
It may be gathered from the foregoing that I have not been able, either in rabbits’ or human embryos, to confirm Balfour’s assertion that the glomeruli receive the testicular tubules.
We are now in a position to mark what becomes, in the male, of the sexual and urinary portions of the Wolffian body. The sexual tubules become the vasa efferentia, whilst the urinary tubules may persist, and constitute the well-known organ of Giraldés. Some of them may even grow, and persist as the vasa aberrantia. These tubules, when present, vary in number, and one of our pupils, Mr Stanley, has dissected a testicle for me, in which four can easily be made out. This is such an unusual circumstance that I have made a sketch of the specimen (fig. 36).
Explanation of Plate II
Fig. 23. Glomerulus of human Wolffian body. Gl, glomerulus ; 7, Wolffian tubule; V, afferent and ‘efferent vessels. 7 Hartnack. 4 Eye p.
Fig. 24. Glomerulus of human Wolffian body, seventh week, showing the commencement of the development of capillaries in the glomerulus, the formation of the parenchyma and the tubules. P, parenchyma; 7’, tubule; Gi, glomerulus; C, capillaries ; £, epithelium of a commencing tubule. 7 Hartnack. 4 Eye p.
Fig. 25. Glomerulus of human Wolffian body at tenth week, showing vascularity of glomerulus and stroma of Wolffian body. Pr, parenchyma; Gi, glomerulus; WZ, Wolffian tubule. 7 Hartnack. 4 Kye p.
Fig. 26. Sexual eminence of rabbit, ,4, in oil immersion, to show relation of surface epithelium to meshes of stroma. This drawing was from a section close to that shown in fig. 37, p. 48.
Fig. 27. Urogenital ridge of rabbit, beginning of thirteenth day. M, mesentery; GH, germinal epithelium; WZ, Wolffian tubule ; WD, Wolffian duct; AO, aorta. 7 Hartnack. 4 Eye p.
Fig. 28. Human embryo, sexual eminence. GH, germinal epithelium ; CV, cardinal vein; WD, Wolffian duct; Gi, glomerulus. The bulk of the urogenital ridge and its genital eminence consists of mesoblastic cells of various shapes—round, branched, and elongated ; these have not been delineated. 7 Hartnack. 4 Eye p.
Fig. 29. Kidney and hinder part of the Wolffian body of a rabbit of thirteenth day. AB, kidney blastema; U, ureter; LCT, loose tissue, which surrounds kidney blastema ; WD, Wolffian duct; W7;, Wolffian tubules; PC, peritoneal cavity. x 70.
Fig. 30. Rabbit, fourteenth day, to show relation of hinder part of the Wolffian body and genital mass to one another, and to the kidney which has just appeared. GJ, genital mass; AO, aorta; XK, kidney ; HZ, hind limb; M, mesentery. x 25.
Fig. 31. Human embryo, thirty-five days. GW, genital mass ; K, kidney, lower end; AO, aorta; CV, cardinal vein; WZ, Wolffian tubules : ; Gl, glomerulus. x 45.
Fig. 32. Genital mass of rabbit, commencement of fourteenth day, to show stroma of branched anastomosing cells, and large, pale, granular cells in its meshes, 7 Hartnack. 4 Eye p.
Fig. 33. Testicle and epididymis of human embryo, at about the twelfth week of intrauterine life. The section is not quite longitudinal. x 25. SZ, seminal tubules; RT, rete testes; Mesor., mesorchium ; Vas. Def., vasa deferens; VE, vasa efferentia; I7, indifferent tissue ; 7A, tunica albuginea.
Fig. 34. Outermost and front part of the same human Wolffian body as that which has been drawn in fig. 39, p. 61. WD, Wolffian duct; C7, collecting tube; ZZ, tubuli efferentia; GM, genital mass. x 45.
Fig. 35. Human foetus, eight months, to show the cell strings of the mediastinum testes which unite tubules of epididymis to seminiferous tubules. 7'H, tubules of epididymis; M7’, mediastinum testes; ST, seminal tubules; V, blood-vessels. x 45.
Fig. 36. Human testicle showing four vasa aberrantia. 17, testicle; Hy, hydatid of Morgagni; VD, vas deferens; Hp, epididymis ; 1, 2, 3, and 4, vasa aberrantia.
Cite this page: Hill, M.A. (2023, December 9) Embryology Paper - Development and transition of the testis, normal and abnormal 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Development_and_transition_of_the_testis,_normal_and_abnormal_2
- © Dr Mark Hill 2023, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G