Book - The Development of the Albino Rat 7

From Embryology
Embryology - 19 May 2019    Facebook link Pinterest link Twitter link  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)

Huber GC. The Development of the Albino Rat (Mus norvegicus albinus). (1915) J. Morphology 26(2).

Normal: Introduction | Materials and Methods | Ovulation, Maturation and Fertilization | Pronuclear Stage | Segmentation Stages | 2-ceIl stage | 4-ceIl stage | 12 to 16-ceIl stages | Summary of segmentation stages | Completion of segmentation and blastodermic vesicle formation | Blastodermic vesicle | Late stages blastodermic vesicle | Egg-cylinder formation | Late stages in egg-cylinder | Conclusions | Literature cited | Figures
Abnormal: Introduction | Half Embryos in Mammalia | Degeneration of ova at the end of segmentation | Incomplete or retarded segmentation | Abnormal segmentation cavity formation | Degeneration of ova as a result of pathologic mucosa | Imperfect development of ectodermal vesicle | Two egg-cylinders in one decidual crypt | Conclusions | Literature cited
Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Late Stages of Blastodermic Vesicle,Beginning of Extypy of Germ Layers

The material at hand is listed in table 7.

Table 7

RECORD NUMBER


AGE


XUMBER OF VESICLES


46


6 days, 14 hours


10


54


6 daj's, 16 hours


9


67


6 days, 16 hours


7


24


6 days, 17 hours


3


90


6 days, 17 hours


6


72


7 days


9


80


7 days


9


92


7 days


6 Total 59


The fixation of the blastocysts of the albino rat obtained during the seventh day after insemination was much more readily accomplished than in those obtained during the preceding day. Of the 59 vesicles of this stage obtained, many show excellent fixation. The thin wall of the vesicle is no longer so prone to fold as in the preceding stage, and does not readily retract from the uterine epithelium or mucosa, no doubt owing to a distinct adhesion of vesicle wall to the maternal tissue. It is difficult, however, so to orient the vesicles as to obtain sections of a desired plane. The general position of a given vesicle is readily determined, since the enlargement of the uterus marking its location is very evident. The vesicles are located in approximatety cylindrical cavities, known as decidual crypts, which are directed toward the antimesometrial border.


These decidual crypts communicate with the lumen of the uterus, which lies eccentric and nearer the mesometrial border, by means of funnel-shaped openings. The decidual crypts or cavities are still lined with uterine epithelium, though this is now much flattened in the immediate vicinity of the vesicle and may be found in part separated from the mucosa of this region. The vesicles are now so placed that in all of them, the thicker portion, the floor of the blastodermic vesicles of younger stages or region of the germinal disc, is directed toward the mesometrial border, thus toward the still patent lumen of the uterus, while the roof of the vesicles is directed toward the antimesometrial border, thus toward the bottoms of the decidual crypts. The general direction of the decidual crypts is in the main at right angle to the long axis of the uterine horn, and directed from the mesometrial to the antimesometrial border. They may deviate, however, from the general direction at various angles and in almost any direction. The decidual crypts as seen in cross section do not as a rule present a circular outline, but appear as sUghtly compressed from side to side, having thus an oval outline as seen in cross section, with the long axis of this oval space as seen in cross section approximately parallel to the long axis of the uterine horn. Since the direction of the decidual crypts can in uncut material be only approximated, the obtaining of sections cut in a desired plane becomes largely a matter of chance. In a large number of my preparations the contained vesicles arc cut in an ohliciuc plane, wiiich may deviate only a little from the longitudinal or may approach a cross axis, while only a relatively small number of vesicles were cut favorably in the lonj^itudiiial plane, and the majority of these are in series cut parallel to the plane of the mesometrium. The vesicles on which the special consideration of this stage is ])ased are reproduced as seen in sections, in fif!;ure 24.


Vesicle A, of figure 24 (rat No. 4(i, () days, 14 hours), is drawn from two successive sections. The upper portion of the figure was drawn under camera lucida from one section, then by superimposing certain of the cells so as to give proper orientation, the lower half of the figure was added from the succeeding section. The slightly oblique plane in which this vesicle was cut made this procedure desirable. This relatively small vesicle seems in excellent state of fixation, as is evident from the symmetrical outline shown by the successive sections of the series. When compared with vesicle E of figure 23, though the two are separated in time of development b}" only a few hours, it is evident that a distinct advance in development has taken place. The so-called floor of vesicle A, the region of the germinal disc of former stages, directed toward the mesometrial border, is markedly thickened, resulting in an outgrowth toward the mesometrial border and an ingrowth into the cavity of the vesicle. The outgrowth forms the anlage of the 'Trager' (Selenka) or the 'ectoplacental cone' (Duval), and appears to have developed largely as a result of an increase in size of the more superficially placed cells, since cell proliferation is not marked in this region. It is admitted that the critical stages are here lacking in my material. These stages appear to fall to the earlj^ hours of the seventh day, the material for which is lacking.

600px

Fig. 24 Sections of blastodermic vesicles or blastocA-sts of the albino rat showing the earl}' stages; of entypj- of the germ disc. X 200. A and B, rat No. 46, 6 days, 14 hours; C, rat Xo. 54, 6 days, 16 hours; ect.pl., ectoplacental cone or TrJiger; ect.n., ectodermal node; -p.ect., parietal or transitory ectoderm; v. ent., visceral layer of entoderm; p.ent., parietal entoderm.


As may be seen from the figure, the cells constituting the anlage of the ectoplacental cone are of relatively large size with large vesicular nuclei, and are continuous at the base with the parietal ectodermal cells which form the roof of the vesicle or its antimesometrial portion. In the cell mass which extends into the cavity of the blastodermic vesicle or blastocyst in which there is recognized the anlage of the 'egg-plug' — 'Eizapfen,' or 'egg cylinder' — 'Eicylinder' (Sobotta) there is evident a fairly clearly circumscribed compact mass of cells, which stain somewhat more dceph' than the surrounding cells and which may be designated as the ectodermal node. It represents the anlage of the true ectoderm of the embryo, as may here . be stated in anticipation of further description. In all of the vesicles of this stage of development, even when cut obli(iuely or in cross section, this small nodule of compactly arranged cells is evident. It is circumscribed both from the cells of the ectoplacental cone as also from the cells lining the blastocele. The metamorphosis leading to the formation of the ectodermal node will receive consideration in a brief general discussion of this stage. The cells covering the egg-plug, and surrounding the ectodermal node, so far as it extends into the blastocele, are arranged in a single layer, forming a dome-shaped membrane, which appears as forced into the cavity of the vesicle consequent on development of the ectodermal node. This layer of cells constitutes the yolk entoderm, the anlage and difTerentiation of which has been previously considered. The antimesometrial portion of this vesicle, its roof, consists of a single layer of somewhat flattened cells, the parietal or transitory ectoderm. The parietal ectoderm presents on its inner surface a few — four in the section figured— entodermal cells of irregular outline. These may be designated, after Sobotta, as cells of the parietal entoderm.


Vesicle B, of figure 24, taken from the same rat as was vesicle A (rat No. 46, 6 days, 14 hours) presents a very favorably cut vesicle, which, however, is slightly compressed from side to side, so that its form appears more nearly circular in the sections cut in the plane of the figure, than were they cut at right angles to this plane. This is especially true of the ectoplacental cone, which for the greater part appears in only two sections of 10 /x thickness, while in the plane of the figure it measures nearly 90 /x. Cognizance of this is to be taken in considering the relative size of the ectoplacental cone as shown in this figure. This vesicle is only very slightly older than that shown in A of this figure. Its ectoplacental cone is made up of a core of relatively large cells, bordered by more flattened cells, which in this preparation stain somewhat more deeply than do the more centrally placed cells. These covering cells are continuous with the cells of the parietal ectoderm. The cell mass projecting into the blastocele is more definitely circumscribed than in the slightly younger stage shown in A of this figure. The ectodermal node appears as an oval mass composed of compactly arranged cells, and is separable on all sides from the surrounding cells. The yolk entoderm, which may now be known as the visceral layer of the entoderm (Sobotta) passes as a single layer of cells of quite regularly cubic or short columnar form, nearly about the ectodermal node to reach the base of the ectoplacental cone, extending over on the parietal ectoderm at one side (see right side of figure). A few of the cells of the parietal entoderm, three in the figure, are evident. The parietal ectoderm forming the roof or antimesometrial portion of this vesicle consists of a single layer of flattened cells, which rest on, and are adherent to the decidual tissue; the uterine epithelium lining the decidual crypt in which the vesicle is lodged having in part disappeared in the immediate region of the vesicle.


Vesicle C of figure 24 (rat No. 54, 6 days, 16 hours) presents a stage which is almost identical in development with that shown in B of this figure, though in shape these two vesicles, as seen in sections, appear quite different. The vesicle shown in C is less compressed than the one shown in B, and probably presents more correctly the form of the blastodermic vesicle or blastocyst of the albino rat at this stage of development. The ectoplacental cone presents a cylindrical outline and contains two cells showing mitotic phases, both included in the section figured. Its cells, more particularly the ones bordering the periphery, present a vacuolated protoplasm, the vacuoles containing lightly colored globules which from reaction to the stain are to be regarded as blood cells or fragments of such, which blood cells are regarded as of maternal origin. In this preparation, the decidual crypt contains a small amount of extravasated maternal blood, found in part surrounding the ectoplacental cone ; also in the antimesometrial portion of the crypt in relation with the roof of this vesicle. These findings will receive further consideration in the succeeding pages. The cell mass projecting into the cavity of the vesicle, consisting of the ectodermal node and the layer of visceral entoderm is slightly larger than in the preceding stage but presents no special features deserving discussion. The vesicle in the section sketched presents very few cells of the parietal entoderm. The parietal ectoderm forming the roof of this vesicle consists of a single layer of flattened cells in the protoplasm of certain of which vacuolization is evident. Certain of the cells show inclusions of lightly staining globules of a color similar to those found in the cells of the ectoplacenta, particularly evident in the lower right of the figure in which they are represented as uncolored circumscribed areas. The color reaction of these globules is like that of the maternal blood cells and fragments of blood cells found in the decidual crypt in the immediate vicinity of the vesicle, and they are regarded as blood cells or fragments of such, taken up by the cells of the parietal ectoderm at this stage in the development of the vesicle.


The blastodermic vesicles or blastocysts figured in figure 24, represent an important stage in the development of the albino rat, as also in a niinilxT ol oilier rodents, in that they show the anlage ot t he plienomenon know'i as t he inNcrsion of the jrefiii layers or ontyi)y ol' Ihef^cnn layers. "Inversion of the ^erni layers — Blattoriunkehruiifi;" in the ova of rodents was probably first rocognizod by Roieheii in the {»;uinoa-pig, niouso, and rat, though it was much more fully and eorrertly (ioseril)ed by BiscliofT as observed in the <2;uinea-pi}2; and a little later by Hensen, also in the <2;uinoa-pis. I'^urther obser\'ations on this phenomenon wore reeord(Ml by Kupffer in his -^tudx" of the de\-elo|)meiit of the field mouse, Arvieola arvalis, and by Fraser on the {jray and white rat and the mouse. Selenka gave this (piestion special study, and in a number of monographic communications deals with the phenomenon of Bliitterumkehrung as observed in three varieties of the mouse, the white rat, and the guinea-pig. Selenka's observations have formed the basis for future work on this probl(Mn. Th(\\' have been widely accepted and extensively quoted. It was he who introduced the term 'Tniger' to denote the cell mass which results from proliferation of the covering cells. His own words concerning this point read as follows:

Wjihrciid hci (Iciii KaiiitirluMiei, nacii erfoljitci' Soiiderunjj; dcr forniativen Fui'('hun<iszellen in ausseivs I'^ktoderni und iiinen's Entoderm,

die gesaniniste Luftc der ausseren Deckzelleii zu einer diinnen resistenten Menibran zusanniieiischrunijjft. verdiokt sicli Ix'i deii Xagern niit invortirten Keiiiihlattcrn der mit den ff)rnKitiven Zellen in Contact bcfindliche Abschnitt der Deckschicht unter l('l)hafter Zellvcrniehrunjj; zu cinoin sphiirischen odcr konischen (lel)il(le, welches ich als 'Trager' bezeichne; * * * * dj^ Einwucherung dieses Triigers ins Inncre der Keiniblase hat zur Folge, dass die scheibenformigen Grundblatter (Ektodenn und Entoderm) sich nicht wie beim Kaninchen zu zwei concentrischer Hohlkugeln erweitern, sondern, ehe sie noch zu diescr Gcstalt gelaiigteii, ins Centrum der Keiniblase vorgeschofen, vorgestiilpt und damit invertirt werden.


In a later publication, this observer also suggested the name 'Entypie des Keimfeldes' as a more comprehensive term than 'Bliitterumkehrung' under which may be included types with inversion of the germ field without actual inversion of the germ layers. In later years Duval, Christiani, Robinson, Jenkinson, Sobotta, Kolster, D'Erchia, Spec, Burckhard, Melissinos, Widakowich, Lee and others have studied the earlier developmental stages of rodents presenting the so-called inversions of the germ layers. O. Hertwig in his chapter "Die Lehre der Keimbliitter" gives a brief resume of our knowledge of the inversion of the germ layers as observed in certain rodents, noting that three main modifications are to be obser^-ed. The first and simplest, as found in the field mouse; the second or intermediate as found in the rat and mouse; the third and most complex as observed in the guinea-pig. Hertwig's account is based largely on the observations of Selenka, the accuracy of which is now questioned from many sides.


In my own conclusions concerning the early stages of the entypy of the germ layers in the albino rat are made on stages which do not portray the very beginning of this process. The vesicles shown in figure 24, in which this process is well initiated, however, present appearances, on the basis of which certain conclusions may be drawn. It is the contention of Selenka that the Trager or ectoplacental cone is developed as a result of proliferation of covering or Rauber's cells, superimposed on the formative cells of the germ disc. He is followed in this view by Jenkinson, who states that "At a certain stage this proximal trophoblast (the so-called Rauber's cells of the rabbit) certainly becomes very thin, but it never wholly disappears, and soon thickens again to form the Trager, or. to use a modern expression, trophoblastic syncytium, which is destined to play an all-important part in the formation of the placenta." The account of ^Nlelissinos is difficult to follow, owing to his application of the term 'Raubersche Schicht.' The outer layer of the blastocyst in the region of the germinal disc is said to have a transitory existence and to disappear almost completel}^ in the earlier stages of blastocyst formation. In a later paragraph he states, dass nur die Raubersche Schicht existiert und sogar in den folgenden Stadien mit zahlreicheren Kernteilungsfiguren, und dass sie den Placentarconus liefert." Attention has previously and on a number of occasions been called to the fact that in the albino rat I have not been able to differentiate a distinct covering layer — Deckschicht or Rauber's Schicht (Selenka); trophoblast layer (Jenkinson) — and have expressed myself as wholly in accord with Sobotta's observations on iho mouso egp; as coiircrns this point. Uo has critically rcvicwiMl Sclcnka's and .Jcnkinson's contr'ntions as to the p;ir1 icipat idii of the coNci'lii^- layci- in the toniialioii of the 'J'n'i^cr or ectoijiaccntal cone, reachinji; the conclusictn that there is no (evidence in support of this. In accord with Duval and in this I concur — he states: "Die mesometrale S|)itze des 'Tracers Selenkas' ist, wie auch Duval lichtiii hcincrkt. so^ar Sanz auffalliii; arm an Mitosen." The anlage of the ectoplacental cone or Tracer, it would appear to me, is |)riinarily the result of enlargement of its constituent cells, this ciilaruciiiciit f)l' cells involving the more peripherally placed cells of the somewhat thickened germinal disc. In none of my i)rei)arations showing early stages in the formation of this structure aic mitotic figures evident. (Jrosser in his figures 67 and li:-5. shows a geiininal vesicle of the albino rat of ()', days in its normal position in the decidual crypt. The vesicle there figured is about identical in time and stage of development to those figured by inc in figure 24. In his figures, the Triiger (Tr.) is represented as consisting of relativel}^ few cells in which no mitoses are evident. In slightly older stages after the means of nutrition of the vesicles is improved through ingestion of maternal blood cells (Sobotta) mitotic figures may be observed in the ectoplacental cone, as shown in C of figure 24. In the rat as in Mus sylvaticus and the guinea-pig (Selenka) the ectoplacental cone arises as a solid mass of cells; in Arvicola arvalis (Kupffer) it is at first a hollow structure and is in part formed by invagination; in the white mouse (Sobotta) the form of this cell mass may vary greatly and may be solid or penetrated by a mere slit or again by a more extensive cavity.


The earlier stages in the formation of the egg-i)lug or eggcylinder I have not been able to follow. In the youngest stage showing this, at my disposal, A of figure 24, it consists of a central node of compactly grouped cells, of polyhedral form, quite definitely demarked from the surrounding cells, and very generally of oval form. This mass of cells I hav(^ designated the ectodermal node. In Grosser's figures f()7 and 113, e, Ec) an identical structure may be observed, designated as 'Ectoderm der Embryonanlage.' The same may perhaps be observed in figure 26, plate 14, of Selenka's account. In figures 26, 28, 31, and 33 of Christiani's contribution this may be postulated, though his figures are useless for a close comparison. Duval does not figure this stage. Sobotta's ('03) figure 7, and figure 33 of the contribution of Melissinos, appear to give a corresponding stage for the mouse, but in neither of these figures is the 'ectodermal node' so clearly depicted as in Grosser's and my own figures, at least not until a somewhat older stage. Figure 6 of Sobotta ('03) may very probably be regarded as representing an intermediate stage between that shown in E of figure 23 and in A of figure 24. By a proliferation of the cells of the germinal area as shown in the former figure a stage resembling that shown in Sobotta's figure 6, is readily postulated. That the formation of the ectodermal cells is in part due to rearrangement of the cells of the germinal area I believe to be the case, since cell proliferation is not marked in this stage. The enlargement of the more peripheral cells of the germinal area, leading to the anlage of the ectoplacental cone, would of necessity cause the forming ectodermal node to force the yolk entoderm into the cavity of the vesicle, and thus form the anlage of the egg-plug and initiate the phenomenon of entj'py of the germ layers. O. Hertwig, in describing the inversion as observed in the mouse and rat, after considering the formation of the Trager through proliferation of the cells of the Deckschicht, following here Selenka's account, states, referring to the Trager, "Durch ihn wird der formative Teil des Ektoblasts nach dem Centrum der Blase vorgetrieben, wobei er sich in eine allseits abgegrenzte Epithelkugel umwandelt." And again, in referring to the development of the guineapig, he states: "Wie bei Maus und Ratte zieht sich das formative Ektoderm zu einer Epithelkugel zusammen." Hertwig thus appears to regard the formation of the 'Epithelkugel,' the ectodermal node, as in part at least developed owing to a rearrangement of the cells of the germinal disc. After the formation of the egg-plug or egg-cylinder that portion of the yolk entoderm which covers it is designated by Sobotta as the visceral layer of the entoderm. The scattered entodermal cells, attached here and ihvrv to the inner suiImcc of tlic |);iric1;il cctoderiii, in the albino rat at no time loiii)i!i<i, ;i cont imions l;iyci-, he lias designated as the parietal (Mitodci-ni. He is ln||(»\vc(l ill llii- I)y A\idakowif'h. This nomonciaturc has been used by nic in the sense enii)loyed by Sol)otla. the parietal or transitory eetodei-ni (Kolster's 'feinfasserige Hant") forniinj;- tiie i-oof or ant iniesonietrial portion of the vesicles, is constituted of a single layer of flattened cells, wiiicli in the rat show no regional differentiation. The resorption of maternal blood, ineidentall.N- noted with reference to cells of the ectoplaeental cone and certain of the cells of the parietal ectoderm in connection with vesicle (" of figure 24, to which i)henom(>non attention lias been drawn by Sobotta and Kolster for the mouse, will receive fnither consideration in the discussion of older- stages.




Normal: Introduction | Materials and Methods | Ovulation, Maturation and Fertilization | Pronuclear Stage | Segmentation Stages | 2-ceIl stage | 4-ceIl stage | 12 to 16-ceIl stages | Summary of segmentation stages | Completion of segmentation and blastodermic vesicle formation | Blastodermic vesicle | Late stages blastodermic vesicle | Egg-cylinder formation | Late stages in egg-cylinder | Conclusions | Literature cited | Figures
Abnormal: Introduction | Half Embryos in Mammalia | Degeneration of ova at the end of segmentation | Incomplete or retarded segmentation | Abnormal segmentation cavity formation | Degeneration of ova as a result of pathologic mucosa | Imperfect development of ectodermal vesicle | Two egg-cylinders in one decidual crypt | Conclusions | Literature cited
Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Cite this page: Hill, M.A. (2019, May 19) Embryology Book - The Development of the Albino Rat 7. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_Development_of_the_Albino_Rat_7

What Links Here?
© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G