Licence: Public Domain Mark
Credit: Researches in embryology. (Second series) / by Martin Barry. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![pared with Plate VIII. fig, 130 (which represents an ovum of the Tenth Stage), there will be found this difference ; that in the space between the membrane of each vesicle and its nucleus there are seen in the present instance (fig. 129.) a number of dark globules, not present as such in the earlier stage (par. 180.). 191. Von Baer appears from his description-f- to have met with ova of the Dog in either this or a neighbouring stage; though certainly no drawing given by that emi- nent observer enables me to recognise the resemblance. He mentions having ob- served a mass of granules, wdiich was conical in the minuter ova, and in those more advanced discoid in its form. Sixteenth Stage of Development. 192. The layer of vesicles am. in the ovum Plate VI. fig. 116, appeared to be passing into the condition of a membrane. Those parts of that layer which formed the sides of the area pellucida {a. p.) were raised and approaching one another, while at the ends of that pellucid space there was no such tendency, but, on the contrary, the appearance of depression into a sort of channel. The sides, here seen to have been in near approximation, appear subsequently to come into contact and unite (Plate VII. fig. 121 D.). (If this supposition be correct, Plate VII. fig. 122—repre- senting a much later stage—shows this union to have taken place at one point; and in figs. 121 A. and 121 B. the union has been more extended. In fig. 122. there is seen a circular space on each side of the point of union. These circular spaces seem to I'epresent the parts which in the sixteenth stage had the appearance of being de- pressed into a sort of channel, or in other words, exhibited no tendency to become raised over the area pellucida). SeventeentJi Stage of Development.— Central and Peripheral Portions of the Germ.— Origin of the Lamina subsequently vascular. 193. About this time the germ separates into a central and a peripheral portion. In the figure representing the present stage (Plate VI. fig. 117-) the ovum is seen in profile, and the germ therefore is not visible. (An idea may be formed of the sepa- ration here mentioned from Plate VIII. fig. 148, in which bh^ is the central, and bh^ the peripheral portion of the germ:|:.) t Lettre, &c., p. 12, X The germ is here represented in its vesicle as seen while still in the centre of the ovum. (The mulberry- like structure was imperfect, and hence the possibility of seeing the objects in its interior.) In this instance the incipient separation of the germ into a central and a peripheral portion appeared to have been premature. These central and peripheral portions of the germ are represented in Plate VII. figs, 121 A. 121 B, and 122. b¥ and bb. Whether they really arise from a separation of the object bb (Plate VI. fig. 113 to 116.) into two ])ortions, future observation must decide. Possibly the object bb disappears by liquefaction, and a linear trace, corresponding to the primitive trace of authors on the Bird, arises in its place. In either case, however, the terms central dcaA peripheral portion of the p^em will be useful in the present memoir, and in either case the embryo does not arise in the substance of a membrane. ,](https://iiif.wellcomecollection.org/image/b2197214x_0028.jp2/full/800%2C/0/default.jpg)
