OF THE VERTEBRATE OVARY. 597 



them, from which they are distinguished, not only by their size, 

 but by their granular nucleus and abundant protoplasm. They 

 are in fact undoubted primitive ova with all the characters which 

 primitive ova present in Elasmobranchs, Aves, &c. In a fairly 

 typical primitive ovum of this stage the body measures O'O2 mm. 

 and the nucleus 0*014 mm. In the inner part of the germinal 

 epithelium there are very few or no cells which can be dis- 

 tinguished by their size as primitive ova, and the cells them- 

 selves are of a fairly uniform size, though in this respect there is 

 perhaps a greater variation than might be gathered from fig. 3/A. 

 The cells are on the average about O'Oi6 mm. in diameter, and 

 their nuclei about o - oo8 0*001 mm., considerably larger, in fact, 

 than in the earlier stage. The nuclei are moreover more granular, 

 and make in this respect an approach to the character of the 

 nuclei of primitive ova. 



The germinal epithelium is still rapidly increasing by the 

 division of its cells, and in fig 37 A there are shewn two or three 

 nuclei in the act of dividing. I have represented fairly accurately 

 the appearance they present when examined with a moderately 

 high magnifying power. With reference to the stroma of the 

 ovary, internal to the germinal epithelium, it is only necessary 

 to refer to fig. 37 to observe that the tubuliferous tissue (/) 

 forms a relatively smaller part of the stroma than in the previous 

 stage, and is also further removed from the germinal epithelium. 



My next stage is that of a young rabbit two days after birth, 

 but to economise space I pass on at once to the following stage 

 five days after birth. This stage is in many respects a critical 

 one for the ovary, and therefore of great interest. Figure 38 

 represents a transverse section through the ovary (on rather a 

 smaller scale than the previous figures) and shews the general 

 relations of the tissues. 



The germinal epithelium is very much thicker than before 

 about 0-38 mm. as compared with O'22 mm. It is divided 

 into three obvious layers: (i) an outer epithelial layer which 

 corresponds with the pseudo-epithelial layer of the Elasmobranch 

 ovary, average thickness 0x33 mm. (2) A middle layer of small 

 nests, which corresponds with the middle vascular layer of the 

 previous stage; average thickness O'l mm. (3) An inner layer 

 of larger nests; average thickness 0^23 mm. 



