OF THE VERTEBRATE OVARY. 599 



stellate, and in a certain number the nucleus has assumed a 

 reticular structure characteristic of the young permanent ovum. 



In addition, however, to the cells which are becoming con- 

 verted into ova, a not inconsiderable number may be observed, 

 if carefully looked for, which are for the most part smaller than 

 the others, generally somewhat oval, and in which the nucleus 

 retains its primitive characters. A fair number of such cells are 

 represented in fig. 38 15. In the larger ones the nucleus will 

 perhaps eventually become modified ; but the smaller cells 

 clearly correspond with the interstitial cells of the Elasmobranch 

 germinal epithelium, and are destined to become converted into 

 the epithelium of the Graafian follicle. In some few instances 

 indeed (at this stage very few), in the deeper part of the germinal 

 epithelium, these cells commence to arrange themselves round 

 the just formed permanent ova as a follicular epithelium. An 

 instance of this kind is shewn in fig. 38 B, o. The cells with 

 modified nuclei, which are becoming permanent ova, usually 

 present one point of contrast to the homologous cells in Elas- 

 mobranchs, in that they are quite distinct from each other, 

 and not fused into a polynuclear mass. They have around 

 them a dark contour line, which I can only interpret as the 

 commencement of the membrane (zona radiata ?), which after- 

 wards becomes distinct, and which would thus seem, as Foulis 

 has already insisted, to be of the nature of a vitelline mem- 

 brane. 



In a certain number of instances the protoplasm of the cells 

 which are becoming permanent ova appears, however, actually to 

 fuse, and polynuclear masses identical with those in Elasmo- 

 branchs are thus formed (cf. E. van Beneden 1 ). These masses 

 become slightly more numerous in the succeeding stages. In- 

 dications of a fusion of this kind are shewn in fig. 38 B. That 

 the polynuclear masses really arise from a fusion of primitively 

 distinct cells is clear from the description of the previous stages. 

 The ova in the deeper layers, with modified granular nuclei, 

 measure about 0*016 C'O2 mm., and their nuclei from o'Oi- 

 O'OI2 mm. 



With reference to the tissue of the hilus of the ovary, it 

 may be noticed that the tubuliferous tissue (/) is relatively 



1 /(V. fit. 



