Book - Contributions to Embryology Carnegie Institution No.23
A human embryo before the appearance of the myotomes
By N. William Ingalls.
With four plates and five text-figures.
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Introduction
The specimen which forms the subject of this paper came into my possession some time ago through the kindness of Dr. E. Peterka, of Cleveland. In the collections of embryology and teratology of the Department of Anatomy of Western Reserve University it is listed as embryo No. 1. On account of the very interesting and important stage of human development which it illustrates, a detailed investigation of its more essential features, esiDecially as regards the embryo proper, has been undertaken. The extra-embryonic structures, chorion, body-stalk, and yolk-sac, and the evidence they offer on early blood and bloodvessel formation, will not be dealt with in detail at this time.
The intact ovum, when it came into my hands, had been for about a month in alcohol of unknown strength, but was, on account of its small size, quite well preserved. The following brief history accompanied the specimen:
April 2. Intercourse (also about two weeks before?). April 8. Period expected; regular 24 to 26 days. April 14. Bleeding commenced, gradually increasing. April 17. Ovum cast off.
Before entering upon a discussion of the anatomical findings, something may be said as to the probable age of the specimen. Following the example of Bryce and Teacher (1908), which has been adopted so frequently, one can set up a similar table for the embryo in question :
The estimated age of 17 to 18 days was put in parenthesis in the above table
because we could not bring ourselves to look upon it with any very great degree of
confidence. The figures were obtained by comparison with embryos which were
obviously in a stage of development either more or less advanced and by reference
to the recent estimates of Triepel (1914) and Grosser (1914). Triepel's suggestion
of subtracting about 18 days from 34 in this case would give an age of about 16 days.
Embryo No. 1 is far in advance of both that described by Fetzer (1910) and the v.
Herfi" embryo of Graf Spee (1896), the ages of which have been given as 15 and 17 to
18 days respectively. On the other hand, it is distinctly less advanced than Frassi's (1907) specimen, the age of which is estimated at (18) 19 days. The embryo
Kl. 13 of Grosser (1913) is strikingly like our own, but we think a trifle more developed. Grosser gives the age as 19 days. A very similar stage of development is
represented by the recent embryo of Strahl (1916), but concerning which there are
no data as to age.
If one again adopt the method of Bryce and Teacher, it is possible to determine when, as regards the menstrual cycle, fertilization took place. The duration of the menstrual cycle in this case may be taken as 25 days regular 24 to 26 and if we let the age of the embryo be 18 days, then fertilization occurred on the seventeenth day of the previous menstrual month. Such a date would harmonize very well with the findings of Frankel on ovulation, as interpreted by Grosser. The time thus assigned for fertilization could easily be pushed still farther toward the beginning of the menstrual month by either supposing that the embryo is more than 18 days old or that development was arrested by the hemorrhage some time before abortion occurred. As regards the last point, we see no reason to suppose that development stopped very long before the ovum was expelled. Fertilization on the seventeenth day of the menstrual cycle would mean that the intercourse of April 2 could not be considered in computing the age, since it falls on the twentieth of the cycle, 15 days prior to the abortion.
The history of intercourse two w'eeks before the one just noted is, however, subject to doubt; it would have occurred on the sixth day of the cycle. This would have called for a rather protracted sojourn of the si)ermatozoa within the tube namelj', 11 days, a period over which they arc doubtless quite cai)al)lc of retaining their fertilizing ])ower. The sixth day of the cycle w'ould fall about the beginning of the so-called period of oestrus, and, in view of the reputed increase in libido at this time and of certain obstetrical experiences, one may suppose that not only is this a favorable time for insemination, but also favorable to a prolonged stay of the spermatozoa within the tubes.
The arrival of the ovum in the uterus and the date of its implantation are dependent ujion the unknown factor of the time consumed in traversing the tube. Grosser points out that this may vary, depending upon tubal (menstrual) conditions, and he is inclined to raise the estimate of 10 days, given bj' himself and Triepel, to 14 days or even more. In either case, implantation would have occurred after the beginning of the lap.sed period, and some influence other than that of the actual ovum upon the uterine mucosa would have to be invoked to inhiliit the ini])ending menstruation. Such an influence, as is well known, has been .sought in the tiny ovum within the tube, acting alone or in conjunction with the newly formed corpus luteum. Assuming 10 days as the period of migration (7 days in the table of BryceTeacher), implantation would have occurred in our si)ecimen on the second day of the cycle. It would therefore have found a nuicous membrane especially adapted to its nutritional needs, possibly thus accounting for its large size as comjjared with the stage of development; but, on the other hand, the inhibitive action upon this same mucosa, from whatever source, may have come too late to save it, as seems also to have been the case with the Bryce-Teacher ovum.
It is not the purpose of this paper to enter into any discussion of the relations between ovulation and menstruation, the passage of the ovum along the tube, or other mooted questions which may have a bearing on the age and development of embryos, but a few words might be said regarding what seem to us to be certain aspects of this subject. Of the three cardinal embryonic features so often quoted, viz, age, size, and stage of development, only the last has any great practical importance, and even here there is more or less variation in different parts of the embryonic body. The fact that age, size, and development by no means rim parallel has been pointed out very clearly by Mall (1914; cf. also Rabl, 1915), and indeed there is no reason to expect that they would be exactly comparable. It seems to us that with ova of the same age, dating from the time of fertilization, discrepancies in their size and development may, and not without reason, be assigned to different environmental factors. Tubal conditions during migration, varying at different times in the menstrual cycle, might play a certain role, resulting in more or less rapid progress along the tube, accelerating or retarding development. Conditions in the uterus at the time of implantation, premenstrual, menstrual, or postmenstrual, etc., time of ovulation, or conceivably the actual size or potcntialitj' of the ripe unfertilized ovum and other unknovai or unappreciated factors, might bring about the variations so often observed. The relative independence of age, size, and degree of development is most strikingh- evident in the case of pathological ova.
The variation in size at the same developmental stage is especially marked in the case of embryo No. 1 (see page 116). The chorionic vesicle is roughly of the same dimensions as that of the embryo Kl. 13 of Grosser or of the embryo of Eternod (1898), while the blastoderm of Xo. 1 is, as well as can be determined, about twice as long as in Grosser's case — but of about the same stage of development and a half longer than in Eternod's — but far less advanced. In other words, the size of the vesicle is fairly commensurate with the assigned age, while the embryo is disproportionateh' large, both as regards the chorionic sac and the estimated age; it is, in addition, very large, considering the degree of development. The opposite disproportion between the sac and contained embryo is quite characteristic of pathological ova, and it may be that we are dealing here with the results of some subtle influence which has stimulated the growth of the embryo proper without, however, having disturbed unduly its orderly development or brought down the balance on the pathological side. A retardation in development but not in growth might account for observed conditions. In the face of the extensive literature on the early chapters of human development we can not claim to present a typical embryo of the middle of the third week, but simply a normal specimen of about that age. It is difficult enough to find one's way among the unnumbered variations of adult morphology, but as regards the embryo we have hardly scratched the surface. It would not be surprising if we had before us in this specimen one of those examples of embryonic variation which are so abundantly present later on (tail, pronephros, milk-ridge, fifth aortic arch, etc.j. For obvious reasons these individual variations become more plentiful as development proceeds, but at no time need they occasion any surprise and always may they be ranged under the same rubric.
One carries away from the perusal of the hteratiire loearing on the age of young ova — the rehitions between ovulation, menstruation, fertilization, implantation, etc. — the impression that the actual age of a normal embryo has a value, for purposes of classification at least, more apparent than real if not in large measure fictitious, and the more so because this assigned age can be only a more or less defensible aj)i)ro.\imation. Complicating the more general factors touched upon above are the individual variations and pccuharities, pathological states it may be of the maternal organism if not also of the future ovum, temporary bodily or seasonal conditions and the like, not to mention possible paternal influences, a variety of factors which it is difficult or impossible to evaluate, and we are imperceptibly carried into problems of fecundity, absolute and relative sterility, and other clinical, racial, and sociological questions. In the end one can appreciate the perplexity of Hyrtl when he wrote long ago in his characteristic vein: "So weit ware nun Alles recht. Xur begreifft man dabei nicht, warum die Frauen nicht fortwahrend schwanger sind, imd aus dem Schwangersein ihr Lebelang nicht herauskommen."
The entire specimen was stained in bulk with hematoxylin, and after sectioning at 10 microns was counterstained with eosin-safranin. The plane of section, which it was supposed would be transverse to the embryo, the interior of the vesicle having been examined somewhat before embedding, came out quite obliquely, as can be seen in the various text-figures. While the staining reactions are not always what could be desired, still there is no doubt that the essential features have been preserved. Occasional mitoses are in evidence, as will be noted later.
Content to be added----
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Cite this page: Hill, M.A. (2026, October 13) Embryology Book - Contributions to Embryology Carnegie Institution No.23. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Contributions_to_Embryology_Carnegie_Institution_No.23
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