394 THE DEVELOPMENT OF THE CHICK 
The sexual cords appear within the gonad on the fifth day; 
they are solid cords of epithelial cells that fill up the interior 
of the gonad and cause it to protrude from the surface of the 
Wolffian body (Fig. 226); the cords extend from the germinal 
epithelium, with which they may be in contact, towards the hilum 
of the gonad (represented at this time by the broad surface 
opposed to the Wolffian body), and into the Wolffian body where 
they enter into close connection with the renal corpuscles. In 
the Wolffian body and intermediate zone they are very irregular 
in their course and connected by numerous anastomoses, corre- 
sponding to the rete region of the future testis. Strands of these 
cells pass dorsally, and, according to some authors, form the 
cortical cords of the suprarenal capsules (Fig. 226). 
The following views of the origin of the sexual cords in birds 
have been held: (1) That they arise as outgrowths of the capsules 
of renal corpuscles (Hoffmann, Semon) and the neck of the 
Wolffian tubules also (Semon); (2) that they are ingrowths of 
the germinal epithelium (Janosik); (3) that they differentiate 
from the stroma (Prenant). The subject is a somewhat difficult 
and complicated one, but the view that the sexual cords arise 
as outgrowths of the capsules of renal corpuscles appears to be 
the best substantiated, and brings the birds into line, in this 
respect, with the reptiles and amphibia. Hoffmann’s observa- 
tion that the sexual cords le at first on the lateral side of the 
blood-vessels intervening between the germinal epithelium and 
the Wolffian body, and that the cells of the sexual cords are 
directly continuous with those of the capsules, should be con- 
clusive. If the cords arose from the germinal epithelium and 
grew secondarily through the stroma into the Wolfhan body, 
there should be a stage when they occur exclusively median to 
the blood-vessels intervening between the germinal epithelium 
and the Wolffian body; but such does not appear to be the case. 
The relation of the sexual cords to renal corpuscles, germinal 
epithelium, and suprarenal capsules in Limosa eegocephala is well 
shown in Fig. 226. 
Sexual Differentiation. The period of morphological indiffer- 
ence of the gonad is relatively long and the actual sexual differ- 
entiation appears slowly. It manifests itself (1) in differences in 
the behavior of the germinal epithelium; (2) of the sexual cords; 
(3) larger size of the left ovary and ultimate disappearance of the 
