596 THE STRUCTURE AND DEVELOPMENT 



to the division of its cells, and great masses of these may 

 frequently be seen to be undergoing division at the same time. 

 Of the tissue of the ovary internal to the germinal epithelium, it 

 may be noticed that the tubuliferous tissue derived from the 

 Malpighian bodies is no longer in contact with the germinal 

 epithelium, but that a layer of vascular stroma is to a great 

 extent interposed between the two. The vascular stroma of the 

 hilus has, moreover, greatly increased in quantity. 



My next stage is that of a twenty-six days' embryo, but the 

 characters of the ovary at this stage so closely correspond with 

 those of the succeeding one at twenty-eight days that, for the 

 sake of brevity, I pass over this stage in silence. 



Figs. 37 and 37 A are representative sections of the ovary 

 of the twenty-eighth day corresponding with those of the earlier 



stages. 



Great changes have become apparent in the constitution of 

 the germinal epithelium. The vascular stroma of the ovary has 

 grown into the germinal epithelium precisely as in Elasmobranchs. 

 It appears to me clear that the change in the relations between 

 the stroma and epithelium is not due to a mutual growth, but 

 entirely to the stroma, so that, as in the case of Elasmobranchs, 

 the result of the ingrowth is that the germinal epithelium is 

 honeycombed by vascular stroma. The vascular growths 

 generally take the paths of the lines which separated the nests 

 in an earlier condition, and cause these nests to become the egg 

 tubes of Pfluger. 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 trabeculse, 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 O'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 



