The early development of the cat 3
Embryology - 19 May 2024    Expand to Translate
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Hill JP. and Tribe M. The early development of the cat (Felis domestica). (1924) Quart. J. Microsc. Sci., 68: 513-602.
- 1924 Cat Development: 1. Ovum of the Cat | 2. Process of Cleavage | 3. Formation of the Blastocyst | 4. Discussion | Plates | cat
Chapter Iii.—Formation of the Blastocyst
1. Late Morula and Early Blastocyst Stages from the Uterus
The material available for the study of these stages, of especial interest for the elucidation of the mode of formation of the blastocyst, consists of (a) a series of five eggs from the uteri of Cat 5.1.10, labelled A-E, three from one uterus, two from the other, and ranging from the solid morula, through morulae in which the blastocyst-cavity is appearing to the early blastocyst, and (b) two uterine eggs from Cat 4.6.19. We have not found it possible to make an accurate count of the blasto- meres in these eggs.
Morula 29 (5.1.10 E). Diameter, 0-128 x 0-10 mm. Diameter of morula, 008 x0-072 mm. Zona, 0-0096 mm. Pig. 22, PL 27.
The morula is ovoidal in section (fig. 22) and is separated by a space from the very thick zona. Such a space occurs in all the eggs of this series, though it is quite narrow in blastocyst 82. Whether it is the result of contraction during fixation or represents a fluid-filled space in the living egg, we are unable to determine. We have drawings of some of the morulae of this series, made with the aid of the camera lucida, whilst they were still in the fixative (picro-nitro-osrnic acid), in which the space is clearly shown, and in this connexion it is worthy of note that Assheton (3) states in the case of the Eabbit that ' up to the moment of the beginning of the [blastocyst] cavity . . . the embryo may often be found to be slightly retracted from the zona radiata in the fresh state ' (p. 131). The morula consists of an outer rather more deeply staining layer of trophoblast, more or less clearly marked off from the somewhat lighter-staining mass of central or embryonal cells. The trophoblast appears as a single layer of large cuboidal to more flattened cells with large nuclei and sparse fat-globules. The central mass fills the space inside the trophoblast and is com- posed of large polyhedral or polygonal cells, also with large nuclei and containing fat-globules. Between the cells, as also between them and the trophoblast, are well-marked inter- cellular spaces, some cleft-like, others irregular, no doubt filled with fluid in the living egg. There is already evidence of the commencing degeneration of some of the central cells. In the section following that represented in fig. 22, three such cells with small degenerating nuclei are met with immediately below the trophoblast. In one the cell-body is indefinite, the nucleus is about half the diameter of that of the normal central cell and has its chromatin massed on one side of the nuclear membrane ; in a second the cell-body is again ill-defined, and the nucleus is still smaller, darkly staining, and pycnotic ; in a third the small cell-body contains a correspondingly reduced bilobed and pycnotic nucleus.
One trophoblastic and one central cell are in process of division.
Morula 30 (5.1.10D). Diameter, 0-12 x 010 mm. Diameter of morula, 0-076 x 0069 mm. Zona, 0-012 mm. Figs. 23 and 24, PI. 27.
This morula is very similar to the preceding. The central cells, however, are rather more loosely arranged, the inter- cellular spaces being more marked, whilst there is unmistak- able evidence of cytolysis of certain of the cells (fig. 24). On the right in the figure is to be seen a cell with a quite degenerate deeply staining nucleus, whilst towards the bottom left of the figure are two quite degenerate cells with shrivelled deeply staining nuclei. In the section preceding that represented in fig. 24 occurs a small pycnotic nucleus lying free in a space apparently formed by vacuolation of the cell-body. TAVO of the trophoblastic cells are in mitosis. Sparse fat-globules are present in the trophoblast, but they appear to have largely disappeared from the central cells.
Morula 81 (5.1.10C). Diameter, 0-12x0-11 mm. Diameter of morula, 0084x0072 mm. Zona, 0-012 mm. up to 0-014 mm. Fig. 25, PI. 27.
This morula generally resembles the preceding two, but on one side, between the trophoblast and the central cells, there is now present a continuous somewhat irregular space extending through six sections and containing remnants of a delicate cytoplasmic reticulum and, in fig. 25 towards the left, a small degenerate nucleus. This space is the beginning of the blasto- cyst-cavity. We regard it as being formed partly by the breaking down of certain of the central cells, partly by the flowing together of fluid-filled intercellular spaces. The central cells are separated here and there by irregular intercellular clefts, but on the whole are more compactly arranged than in morula 30. Fat-globules are present both in the trophoblast and the central cells, in the latter in fair numbers. One of the tropho- blast cells is in mitosis.
Blastocyst 32 (5.1.10B). Diameter, 0-108x0-105 mm. Diameter of blastocyst, 0-079 x 0075 mm. Zona, 0-012 mm. Pig. 28, PI. 28.
In this egg the blastocyst-cavity is represented by two spaces of unequal size which extend up on one side of the blastocyst from the lower pole to just past the equator, the sectional plane being apparently transverse to the polar diameter. The spaces lie between the trophoblast and the mass of central cells (fig. 28), and appear empty except for the presence of traces of cytoplasmic detritus adjoining the central cells and, in the larger, of a very degenerate cell-remnant. The central cells are separated here and there by inter- cellular spaces and appear similar except that certain of them have more eosinophil cell-bodies than the others. There is no evidence of degeneration in the main body of the central cells.
Two central cells and one trophoblastic are in mitosis.
Blastocyst 33 (5.1.10 A). Diameter, 012x010 mm. Diameter of blastocyst, 0-08 x 0-067 mm. Zona variable up to 0-012 mm. Fig. 29, PI. 28.
The blastocoele is now a continuous cavity situated in the lower hemisphere of the blastocyst and measuring 0024 x 0043 x 0-048 mm. It is bounded^ below and at the sides by the trophoblast and above by t h e ' mass of central cells. The blastocyst stage is thus definitely established. It consists of the investing trophoblast in the form of a single layer of cells, attached to the inner surface of which, and occupying the upper hemisphere is the embryonal knot or inner cell-mass formed by the central cells of earlier stages.
The trophoblastic cells are now rather more flattened in form, especially where they bound the blastocoele. Four of them are in process of division. In one, in addition to the normal nucleus and in contact with it, there is present a quite small accessory nucleus.
In the blastocyst-cavity there is present what appears to be a mass of cytoplasm about the size of a central cell but non- nucleated ; and on one side, in contact with the trophoblast, is a vacuolated and much degenerate cell with a pale-staining remnant of the nucleus. Further evidence is thus afforded of the occurrence of degeneration amongst the central cells.
The embryonal knot consists for the most part of large cuboidal cells separated here and there and from .the tropho- blast by intercellular spaces. They appear similar in their cytological characters except that some few of them tend to have more definitely contoured cell-bodies and stain rather more deeply with eosin than the others. Two such cells are seen at the lower border of the inner cell-mass in fig. 29, and shortly above them is another definitely contoured cell with an eosinophil cell-body. We suggest that possibly these eosinophil cells are entodermal cells, and that the process of segregation or delamination which results eventually in the formation of a connected layer of entoderm has already commenced.
A somewhat remarkable feature, the significance of which is not clear, is the occurrence in seven of the central cells of a small accessory nucleus adjacent to the normal nucleus and exhibiting obvious signs of degeneration, such nuclei being small and in most cases deeply staining and pycnotic.
A number of cells both trophoblastic and central are in division.
We append here a brief mention of the two uterine eggs from Cat 4.6.19, one of them, A (34), being in the morula stage, the other, B (85), an early blastocyst.
Morula 34. Diameter, Oil x 009 mm. Morula, 0-076 x 0-069 mm. Zona. 0-012 mm.
This morula in its stage of development is very similar to morula 31. What we take to be the commencing blastocyst- cavity is an irregular cleft-like space which reaches the tropho- blast at one end and extends up obliquely between the central cells to terminate near the equator. Certain of the central cells stain rather more deeply and possess more definitely con- toured cell-bodies than the others, and may possibly be the entodermal mother-cells. One such cell is in mitosis.
Blastocyst 35. Diameter, 0-11 x 0-10 mm. Blastocyst, 008 x 0076 mm. Zona, 0-012 mm.
This blastocyst appears to be slightly in advance of blasto- cyst 33, inasmuch as its trophoblastic cells are distinctly more flattened and the blastocyst-cavity is more extensive, but the central cells are much less compactly arranged than in 33, and we question whether the specimen is quite normal. We mention it here because it provides unmistakable evidence of the presence of two varieties of central cells, viz. (a) definitely contoured cells, ovoidal or spherical, with relatively small nuclei and voluminous light-staining cell-bodies, often vacuolated and frequently with one or two minute accessory nuclei, and (b) smaller cells of irregular form with relatively large nuclei and less voluminous, more darkly-staining cell-bodies. Variety (a) appears to be more numerous than (b), otherwise we should have been inclined to regard it as entodermal, but since neither corresponds with the presumed entodermal mother-cells in morula 34 and blastocyst 33, and since we are not satisfied that the specimen is quite normal, we do not venture to suggest which of the two is ectodermal and which entodermal in significance.
2. Formation of the Didermic Blastocyst
Blastocyst 36 (6 A. 6.5.12). Diameter in fixative, 0-25 mm. ; in section, 0-225 mm. Zona, 0-0036 to 0-0048 mm. Figs. 30 and 32, PI. 28.
This blastocyst is, unfortunately, separated by a considerable
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- 1924 Cat Development: 1. Ovum of the Cat | 2. Process of Cleavage | 3. Formation of the Blastocyst | 4. Discussion | Plates | cat
Reference
Hill, J. P., and Tribe, M. 1924. The early development of the cat (Felis domestica). Quart. J. Microsc. Sci, 68, 513-602.
Cite this page: Hill, M.A. (2024, May 19) Embryology The early development of the cat 3. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/The_early_development_of_the_cat_3
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
