424 V. M, BALFOUR. 



tubes of Pfiilger. It is obvious in figure 37 that the vascular 

 ingrowths are so arranged as imperfectly to divide the germinal 

 epithelium into two layers separated by a space with connective 

 tissue and blood-vessels. The outer part is relatively thin, and 

 formed of a superficial row of columnar cells, and one or two 

 rows of more rounded cells ; the inner layer is much thicker, and 

 formed of large masses of rounded cells. The two layers are 

 connected together by numerous trabeculae, the stroma between 

 which eventually gives rise to the connective tissue capsule, or 

 tunica albuginea, of the adult ovary. 



The germinal epithelium is now about 0-19 — 0*22 mm. in 

 thickness. Its cells have undergone considerable changes. A 

 fair number of them (fig. 37 a, p.o.), especially in the outer layer 

 of the epithelium, have become larger than the cells around 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 primi- 

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

 primitive ovum of this stage the body measures 0*02 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 themselves 

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

 a greater variation than might be gathered from fig. 37a. The 

 cells are on the average about 0'016 mm. in diameter, and their 

 nuclei about 0-008 — 0-OOlmm., 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 divi- 

 sion of its cells, and in fig. 37a there are shown 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 {t) 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 3S 

 represents a transverse section through the ovary (on rather a 

 smaller scale than the previous figures) and shows the general 

 relations of the tissues. 



The germinal epithelium is very much thicker than before 



