416 F. M. BALFOUR. 



In the development of the ovary the stroma becomes differ- 

 entiated into an external vascular layer, especially developed 

 in the neighbourhood of the germinal epithelium, and an internal 

 lymphatic i)ortion, which forms the main mass of the ovarian 

 ridge (PL XYII, figs. 2, 3, and 6) . 



(2.) At first the thickened germinal epithelium is sharply 

 separated by a membrane from tlie subjacent stroma (PI. XVII, 

 figs. 1, 2, and 3), but at about the time when the follicular 

 epithelium commences to be formed round the ova, numerous 

 strands of stroma grow into the epithelium, and form a regular 

 network of vascular channels throughout it, and partially isolate 

 individual ova (PI. XVII, figs. 7 and 8). At the same time the 

 surface of the epithelium turned towards the stroma becomes 

 irregular (PI. XA^II, fig. 9), owing to the development of indi- 

 vidual ova. In still later stages the stroma ingrowths form a 

 more or less definite tunic close to the surface of the ovary. 

 External to this tunic is the superficial layer of the germinal 

 epithelium, which forms what has been spoken of as the pseudo- 

 epithelium. In many instances the protoplasm of its cells is 

 produced into peculiar fibrous tails which pass into the tunic 

 below. 



(3.) Frimifive ova. — Certain cells in the epithelium lining the 

 dorsal angle of the body cavity become distinguished as 

 primitive ova by their abundant protoplasm and granular nuclei, 

 at a very early* period in development, even before the forma- 

 tion of the genital ridges. Subsequently on the formation of 

 the genital ridges these ova become confined to the thickened 

 germinal epithelium on the outer aspect of the ridges (PI. XVII, 



fig-1). 



(4.) Conversion of primitive ova into jiermanent ova. — Primitive 

 ova may in Scyllium become transformed into permanent ova in 

 two ways — the difference between the two ways being, however, 

 of secondary importance. 



[a.') A nest of primitive ova makes its appearance, either by 

 continued division of a single primitive ovum or otherwise. The 

 bodies of all the ova of the nest fuse together, and a poly- 

 nuclear mass is formed, which increases in size concomitantly 

 with the division of its nuclei. The nuclei, moreover, pass 

 through a series of transformations. They increase in size and 

 form delicate vesicles filled with a clear fluid", but contain close to 

 one side a granular mass which stains very deeply with colouring 

 reagents. The granular mass becomes somewhat stellate, and 

 finally assumes a reticulate form with one more highly refract- 

 ing nucleoli at the nodal points of the reticulum. When a 

 nucleus has reached this condition the protoplasm around it has 

 become slightly granular, and with the enclosed nucleus is seg- 



