398 THE DEVELOPMENT OF THE CHICK 
During this period the sexual cords become converted into 
the semeniferous tubules, rete, and vasa efferentia; and the 
sexual tubules of the Wolffian body into the epididymis. About 
the end of the third week the sexual cords obtain a lumen, owing 
to rearrangement of the cells; at the same time a basement mem- 
brane appears over the outer ends of the cells, and the semenif- 
erous tubules are definitely established (Fig. 228). In these 
one can easily recognize the descendants of the primitive ova 
which may now be called spermatogonia, and the epithelial or 
supporting cells. The irregularly anastomosing sexual cords in 
the region of the hilus become the rete cords, which acquire a 
lumen shortly after hatching. The rete cords are united to the 
neighboring renal corpuscles by the original strands and these 
form the vasa efferentia. 
As regards the formation of the epididymis: the renal corpuscles 
of the Wolfhan tubules concerned diminish in size, the glom- 
erulus disappears and the cells of the capsule become cylindrical. 
These changes progress from the lateral side of the Wolffian 
body towards the testis; that is to say, the more lateral corpuscles 
are first affected. A rudiment of the non-sexual part of the 
Wolffian body persists in the mesorchium of the male, between 
testis and kidney. It is known as the paradidymis. 
Development of the Ovary. (There is no complete account of 
the development of the ovary in the chick; the following account 
is based on Hoffmann’s description of Grallatores and Natatores.) 
The right ovary may attain a considerable size; but sooner 
or later it degenerates and is never functional; moreover, its 
growth does not follow a normal course of differentiation. The 
description applies, therefore, only to the left ovary. 
In the indifferent gonad, primitive ova leave the germinal 
epithelium and enter the stroma and sexual cords at corresponding 
stages of development whether the organ is to become ovary or 
testis. Such, however, in the case of the ovary, are destined to 
degenerate, along with the sexual cords. The definitive ova 
are derived from primitive ova that have remained within the 
germinal epithelium. 
The characteristic feature of the development of the ovary 
is, then, a cessation of migration of primitive ova from the 
germinal epithelium after a certain stage and a multiplication 
in situ. The epithelial cells of the germinal epithelium share in 
