JOURNAL OF MICROSCOPICAL SCIENCE. 



DESCRIPTION OF PLATE V, 



Illustrating Mr. Poulton's Paper on " The Structures connected 

 with the Ovarian Ovum of Marsupialia and Monotremata." 



Fig. 1. — X 9. Transverse section of the ovary of Phalangista. The figure 

 gives a representation of the appearances seen in an average section of this 

 ovary. Even under this low power there are certain obvious differences 

 between such a section and that of the Mammalian ovary as usually described. 

 This is especially true of tlie larger follicles (F. and F'.), of which the 

 membrana granulosa (M. G.) forms a very thin and regular layer, only marked 

 by slight thickenings at the point nearest to the ovum (o.). The latter is 

 never embedded in the membrana granulosa in the largest follicles, so that the 

 slight thickenings are the only indications of a cumulus proligerus, and the 

 ovum lies in the abundant contents of the follicle. Other differences will 

 appear in the more highly magnified figures, st. Stroma, consisting of fibrous 

 tissue and stroma cells. F. Large follicle, with the included ovum (o) turned 

 towards the outside of the ovary. /. t. Tunica fibrosa, becoming highly 

 vascular close to the follicle, m. g. Membrana granulosa, relatively thin and 

 regular (except near to the ovum), i. I. Intermediate layer, in which the 

 cells of the membrana granulosa are continuous into the contents of the 

 follicle (central substance), c. s. Central substance, very different from the 

 liquor foUiculi of the ordinarily-described Mammalian follicle, both in struc- 

 ture and in the fact that the ovum lies within it. The substance stains with 

 extreme difiiculty, and often not at all. Its external layer is rather darker, 

 bordering on the lighter intermediate layer (but these effects are not due to 

 the staining), while the membrana granulosa stains deeply. The structure 

 and relations of these layers will appear in the more highly magnified figures. 

 F' . Large follicles of similar structure to the one described above, but not 

 cut through in the plane of the ovum. It is seen that as the follicles increase 

 in size they project more and more from the surface. Tlie contents of the 

 follicles have contracted, thus leaving a space between the membrana granulosa 

 and the follicular walls. In one case the membrana granulosa has been 

 thrown into folds. This appearance is different from that seen in higher 

 Mammalia, where the fluid contents of the follicle shrink away from the 

 membrana granulosa (which rarely becomes detached from the follicular walls) 

 in the process of hardening, and probably also drain away to some extent. 

 Here in the large follicles the contents generally fill the space included by the 

 membrana granulosa. F" . Tangential sections through large follicles, in some 



