OVUM. 



59 



Each developed ovule, therefore, in these 

 oviparous animals, comes to be contained in a 

 pediculated capsule, which is formed by the 

 extension of the substance of the ovary ; but 

 from the great extent to which the dilatation 

 of the capsule occurs, the true ovarian stroma 

 is reduced to a very small amount, and 

 scarcely more remaining than the theca of the 

 capsule itself and the ovarian coverings. 



In the other animals possessing the large 

 yolked ova, nearly the same structure of the 

 ovary prevails. In chelonia and crocodiles, 



it is indeed almost identical with that in 

 birds. In lizards and serpents, the hollow 

 state of the ovary produces some difference 

 in the general form ; and in cartilaginous 

 fishes (sharks and rays) other differences in 

 the structure of the ovary may exist ; but in 

 all these animals the essential points of rela- 

 tion between the ovarian substance and cap- 

 sules, and the large ovules, are the same as 

 that now described in birds. 



The lining membrane of the ovicapsule of 

 birds is thick and tough, and on its inner sur- 



Fig. 43. 



Structure of the ovisac in the fowl's ovary. 



A. Inner surface of a portion of the ovisac of a fully-developed ovarian capsule, magnified about six 

 diameters, showing an appearance which might be mistaken for glandular depressions produced by 

 the peculiar disposition of the veins. 



B. The same, from a calyx from which the ovum has been discharged some days before ; a -whitish 

 flaky membrane is deposited on portions of the surface. 



c. The same, from an undeveloped capsule of a quarter of an inch in diameter, across the stigmatic band. 



D. The disposition of the blood-vessels near the stigmatic band, which seems at first sight non-vascu- 

 lar, but is in reality traversed by ramifying small vessels proceeding from the neighbouring larger veins, 

 and crossing the stigmatic band. 



E. Two of the large mouths of the veins, which give the semblance of follicular pits represented in 

 A and c, but which are quite closed, with the smaller vessels ending in them, as' seen from the 

 inner surface of the ovisac. 



face presents a soft appearance somewhat si- 

 milar to that of a mucous membrane. In ex- 

 amining the inner surface of this membrane, 

 Dr. Sharpey and the author had their atten- 

 tion arrested by an appearance such as might, 

 on first sight, be attributed to a number of 

 follicular or glandular pits. This appearance, 

 as we first observed it, is represented \nfig. 43. 

 (A, B, c) as it was seen in a fully-developed 

 capsule in one a third of an inch in diameter 

 and in a calyx from which the yolk had 

 been discharged some days previously. We 

 supposed, indeed, at first that the appearance 

 depended on the presence of the orifices 

 of follicular depressions or glands on the 

 inner surface of the membrane. A more 

 attentive examination of this membrane by 

 Dr. Sharpey has shown that the appearance 

 is not due to depressions of the inner surface 

 of the membrane or to the mouths of follicles 



opening upon it, but is caused by a peculiar 

 form of the blood-vessels seen through the 

 entire and smooth inner surface of the mem- 

 brane. The apparent depressions are in fact 

 the sudden terminations or beginnings of veins 

 of considerable size seen through a delicate 

 and transparent -portion of the membrane 

 which closes them towards the inner surface. 

 They may be made very obvious by merely 

 coarsely brushing the smooth blunt edge 

 of any instrument over the membrane, and 

 thus causing the blood to flow from the 

 vessels in other parts in these sinuses or 

 dilated veins. 



It would appear that the smaller capillary 

 vessels in which the arteries terminate, in ap- 

 proaching the inner surface of the capsule, 

 ramify with considerable minuteness, and at 

 each of the marks or apparent depressions 

 referred to suddenly fall into or end in the 



