Book - The Development of the Albino Rat 12
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Degeneration and Death of Ova at the End of the Segmentation Stages
In figure 2, A and B, are presented drawings of typical sections of two morula masses showing complete degeneration and death. The degenerated ovum shown in A, of this figure was obtained from rat No. 52, 4 days, 15 hours, after insemination. In all, eight normal ova were found in the uterus of this rat, these showing late morula stages and stages of early blastodermic vesicle formation, three of which were sketched and are shown in A, B, and (' of figure 20, Part I. The degenerated ovum here under consideration lies in very close proximity to the normal blastodermic vesicle shown in C of figure 20, Part I. The shallow mucosal pits harboring the two ova are in contiguity. The two contiguous pits resemble each other very much; the mucosa underlying them is in every respect the same, indicating, it would seem, that to a certain stage in development — to the end of segmentation — the development of the degenerated ovum proceeded normally. The degenerated egg-mass measured approximately 80 /z by 50 /x by 40 /x. In reaction to stains, it differs markedly from the adjacent normal vesicle. The staining is very pale; cell boundaries are indistinct or lost, and the nuclei scarcely retain any coloring matter. Scattered through the protoplasm are found small globular masses, perhaps of lipoid character. Protoplasm and nuclei present evidences of cytolysis and chromatolysis, and have the appearance presented by necrotic tissue. Had normal development supervened, both ova
Fig 2 Ova of the albino rat in late segmentation stages, showing death and dissolution of the constituent cells. X 200. A, rat No. 52, 4 days, 15 hours, after the beginning of insemination. B, rat No. 68, 4 days, 16 hours, after the beginning of the insemination. This figure shows an im])erfectly developed morula with probable retention of oolenmia.
(the pathologic and the acljaccnl iiorinnl oiicj would in nil piohubihty have been enclosed within the same decidual ciypt, ;t condition exceedingly rare, judging iVoni the material at hand. Whether the very close proximity of these two ova bears causal relation to the death of one, by reason of the consequent lessening of the available pabulum or embryotroph, can only be conjectured. There is at this stage no question of faidty implantation, the ova, though presumal)ly permanently lodged, He free in the lumen of the uterus. Whether on the other hand, the death of this ovum was the result of some inherent nuti'itional deficit must also remain unanswered. However, this preparation may serve to show that ova of the albino rat, after reaching the uterine tube, and after apparently normal segmentation, may undergo death and dissolution, for reasons which are not structurally discernable.
B of figure 2, rat No. 68, 4 days, 1() hours, after insemination, is from the uterus of a rat containing four ova in early stages of blastodermic vesicle formation, three of which were sketched under D and E of figure 20, and the series of figure 21, Part I. The preparation here described lies free in the lumen of the uterus, and appears to represent an uncompleted segmentation, with cells and nuclei showing cytolysis and chromatolysis. The mass is surrounded by a thin membrane regarded as an oolemma. Normally the oolemma of the segmenting ova of the albino rat is lost in the 4-cell stage, now and again in the 2-cell stage. Whether the retention of the oolemma may be brought in causal relation to the death and dissolution of the enclosed cells is problematic. That such causal relation may exist for the ova of the albino rat, appears to me as not impossible. This degenerated egg-mass presents the only instance of the laie retention of the oolemma in the albino rat material at my disposal.
Incomplete or Retarded Segmentation
The blastodermic vesicles presented in figures 3 and 4 have been interpreted as showing incomplete or retarded division of certain of the cells of early stage morula masses. The probable fate of such blastodermic vesicles in further development cannot be projected with any degree of certainty. The most characteristic vesicle showing this phenomenon is presented in figure 3, and is taken from rat No 53, 5 days after insemination, the uterus of which contained seven blastodermic vesicles showing early stages of development, four of which are reproduced in figure 22, Part I. In A and B of figure 3 are reproduced two consecutive sections of a series of five sections of 10 ju thickness, including this ovum. In the lower part of this ovum there is found a small segmentation cavity, bounded by cells which present normal appearances. The roof of this vesicle is slightly
Fig. 3 Early stages of the blastodermic vesicle of the albino rat, presenting evidence of irregular or retarded segmentation. X 200. Rat No. .53, o days after the beginning of insemination.
Fig. 4 Three ova of the albino rat, showing early blastodermic vesicle stages, in each of which certain of the cells suggest irregular or retarded segmentation. X 200. A, rat No. G4, 4 daj-s, 14 hours, after the l)eginning of insemination. B, rat No. 68, 4 days, 15 liours, after the beginning of insemination. C, rat No. 54, 6 days, 16 hours, after the beginning of insemination.
folded and compressed, as a consequence of which the roof wall in the sections figured is presented in part as seen in surface view. In the floor of this vesicle there is to be observed, surrounded by other smaller cells, one large cell, of nearly spherical shape, having a diameter which is three or four times as great as that of the majority of the surrounding cells. The protoplasm of this large cell stains less deeply than does that of the majority of the other cells constituting the floor of the vesicle. Its nucleus is relatively large and slightly lobulated, so much so that in the section of it shown in A of this figure, in the optical section sketched, the nucleus appears as three separate nuclei, in reality, lobules of the same nucleus. In A of this limine ilicic is shown to the lower left of \hv lar^e eell aiiolhcr rclaliNclx' l.-irjic cell, enelosiiis a <;lol)ular inelusion, which stained faintly, :ni<l tlic nature of which was not fully determined. In the uj)j)er j)art of each of the tw^o figures are seen cells which show cytolysis and loss of nuclei; regarded as degenerating cells, \\licn rompaicd wdth the normal blastodermic vesicles obtained fioni the same uterus, the ovum here described presents a imique a):>))eai-ance. and was readily recognized as showing developincnt and stiuct in-c which deviated from the normal. At this stage of dex'elopment, the blastodermic vesicles of the albino rat are still found lying free in the lumen of the uterus, showing no structural relation to the uterine mucosa. This vesicle has been interpreted as showing irregular or retarded segmentation. It is conjectured that one of the cells, perhaps of the 8-cell stage, did not undergo further cleavage. The large cell presents an appearance evidencing beginning stages of degeneration, and in further development, would probably have undergone dissolution. The majority of the smaller cells of the roof appear as if normal, as do also the cells of the floor, certain of the smaller cells of the floor presenting mitoses as evidence of further proliferation.
In figure 4, A, B, and C, there are presented typical sections of three ova of the albino rat showing what has been regarded as irregular segmentation. A of this figure represents an o\'um taken from rat No. 64, 4 days, 14 hours, after insemination, in the uterus of which there were found five normal ova showing early stages of blastodermic vesicle formation, foui- of wliicli lu-v cut longitudinally, one in a series of cross-sections. In each of the four longitudinally cut series the floor of the respective vesicles is markedly folded, owing to fixation contractions; therefore, flone were sketched as normal stages. In appearance, they resemble closely the vesicles sketched under C, D, and E of figure 20, Part I. In the pathologic ovum, show^n in A of figure 4, there is no evidence of segmentation cavity formation. However, the ovum cannot be regarded as presenting a late morula stage such as is figured in A of figure 20, Part I, since it shows distinct departure from the normal. The marked constriction seen to the lower left of the figure passes through the series of four 10 jd sections including this ovum, and in part separates a portion composed of relatively small cells from a larger portion composed of larger cells. The rate of segmentation of certain of the cells composing the upper larger portion of this cell mass appears to have been retarded, thus retarding the development of the whole mass. This pathologic ovum rests normally in a shallow pit of the mucosa, very similar in form and structure to the shallow pit lodging the five normal vesicles found in this uterus.
The ovum shown in B of figure 4 was obtained from the uterus of rat No. 68, 4 days, 16 hours, after insemination, with four normal vesicles showing early stages of blastodermic vesicle formation. From this uterus was also taken the completely degenerated cell mass with persistent oolemma shown in B of figure 2. This vesicle on superficial observation does not appear to depart markedly from the normal ajipearance for this stage. In form and size it corresponds closely to the normal ova taken from this uterus. The segmentation cavity seems to have developed normally. The slight folding of the roof seen to the left of the figure is accidental, due to fixation shrinkage, and is very similar to folding of the roof to be observed in many of the normal preparations of the series. In the floor of the \'esicle there may be observed three relatively large cells, partly enclosed by smaller cells of a size comparable to that of the cells forming the floor of the normal blastodermic vesicles of this stage of development. The three relatively large cells, clearly distinguished in the figure, are interpreted as showing a retarded segmentation. So far as maj' be determined, their protoplasm and nuclei present normal structure, the lowest of the three cells showing an early mitotic phase. I am inclined to the opinion that this ovum would have continued in development, perhaps in later stages showing distinct arrest in development. This hypothesis seems warranted on the basis of the study of a vesicle shown in C of figure 4, taken from rat No. 54, 6 days, 16 hours, after insemination. Normal stages for the albino rat, taken about the middle of the seventh day after insemination, are shown in figure 24, Part 1. I'(>ferencp to this fif>;ur(' iiiny scia'c to show thai (hiring tho early hours of the seventh day after iiiseniiiial ion, the phenomenon of inversion or enty]\v of the genu layers is initiated in the albino rat. The ova are, on reaching tliis stage of develo])ment, enclosed within a well differentiated decidual crypt wliieh communicates as yet freely with, the lumen of the uterus. These crypts present a continuous lining of uterine epithelium; the ef)ntained ova are thus not as yet in direct relation witli the maternal decidua. In the normal blastodermic vesicle of this stage, the ectoplacental cone is in anlage, and in the cell mass wliich extends into the cavity of the vesicle the egg-plug or cgg-eylinder — there is evident a clearly circumscribed nodule of cells, which has been designated the ectodermal node and recognized as the anlage of the primary embryonic ectoderm; this node is in part surrounded by the yolk entoderm. In the uterus of rat Xo. 54, there are contained nine blastodermic vesicles, one of which is sketched in C of figure 24, Part I. Not nearly all of these \'esicles are so favorably cut as that shown in this figure, the majority being cut in a plane which is oblique to the long axis of the vesicle. However, in all of them the ectoplacental cone and the ectodermal node may be determined except in the one shown in C of figure 4. This vesicle was obtained from a series of sections passing at right angles to the plane of the mesometrium. It lies free in a deep decidual crypt and passes through six sections of 10 yu thickness; thus is compressed from side to side. This vesicle is distinctly smaller than the normal ones taken from this series, especially so as concerns its cavity. An ectoplacental cone is not clearly differentiated, and it is not possible to determine an ectodermal node, nor is it clear that the yolk entoderm has differentiated. In the cell mass from which ectoplacental cone and ectodermal node should have developed, the upper portion of this figure, there are evident, in the sections figured, four relatively large cells with relatively large nuclei, cells which have been interpreted as evidencing retarded segmentation with consequent retardation in the normal differentiation of the vesicle. On tracing this vesicle through the series of six sections it would seem that the direction of section is favorable. The uterine mucosa appears to have reacted normally; the decidual crypt in which this vesicle is lodged presenting normal size and form, and the surrounding decidua normal structure. The vesicle itself is retracted from the uterine epithelium, intact throughout the crypt, thus, does not appear to have attained the normal adhesions observed in normal vesicles of this stage. The four ova depicted in figures 3 and 4, appear to present a distinctive type of abnormal development, a type which is interpreted as showing retarded segmentation in certain of the cells of the S-cell and perhaps 16-cell stage. All are found in uteri containing normal stages. The appearances presented, if correctly interpreted, speak in favor of a structural or metabolic defect inherent in the cells themselves and not primarily dependent on environment, pabulum, or embryotroph.
Fig. 3 Four consecutive sections of the ovum of the albino rat showing abnormal development of the segmentation cavity X 200. Rat No. 46, 6 days, 14 hours, after insemination.
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Cite this page: Hill, M.A. (2020, October 24) Embryology Book - The Development of the Albino Rat 12. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_Development_of_the_Albino_Rat_12
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