426 F. M. BALPOUR. 



number the nucleus has assumed a reticular structure charac- 

 teristic of the young permanent ovum. 



In addition, however, to the cells which are becoming converted 

 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. 38b. 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 folhcle. 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 shown in fig. 

 38b, 0. The cells with modified nuclei, which are becoming per- 

 manent ova, usually present one point of contrast to the homolo- 

 gous cells in Elasmobranchs, 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 FouHs has 

 already insisted, to be of the nature of a vitelline membrane. 



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 Elasmobranchs 

 are thus formed (cf. E. van Beneden).^ These masses become 

 slightly more numerous in the succeeding stages. Indications 

 of a fusion of this kind are shown in fig. 3Sb. That the poly- 

 nuclear 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 — 0'02 mm., and their nuclei from 0*01 — 0'012 mm. 



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

 be noticed that the tubuliferous tissue {t) is relatively reduced in 

 quantity. Its cells retain precisely their previous characters. 



The chief difference between the stage of five days and that of 

 two days after birth consists in the fact that durhig the earlier 

 stage comparatively few modified nuclei were present, but the 

 nuclei then presented the character of the nuclei of primitive ova. 



I have ovaries both of the dog and cat of an equivalent stage, 

 and in both of these the cells of the nests or egg tubes may be 

 divided into two categories, destined respectively to become ova 

 and follicle cells. Nothing which has come under my notice tends 



• Loc. cit. 



