242 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The genital strands are formed rather late in the chick, in the course 

 of the sixth day of incubation. They are true buds of the germinative 

 epithelium, as in Mammals. Their formation is rapid and soon ceases. 

 The connective-tissue of the genital rudiment arises from the sub- 

 germinative mass of mesenchymatous origin from which the urogenital 

 connexions are also differentiated. The derivatives of the germinative 

 epithelium do not share in the formation of the connective cells. With 

 the appearance of the connective trabecule there coincides the appearance 

 of blood-vessels coming from the Wolffian body. 



When the strands of the first proliferation are formed, this ends the 

 period of sex-indifference — on the seventh day. The distinctive sex- 

 characters are at first far from well-marked. The right ovarian primor- 

 dium is seen to be smaller. The young ovary shows, as compared with 

 the young testis, a greater thickness and inequality of the superficial 

 epithelium, a less definite limitation of the medullary strands, and less 

 abundance of connective-tissue. The precocious degeneration of tbe 

 Miillerian duct is the characteristic sign of the male sex. 



In the embryo of eleven days the ovarian rudiment of the chick 

 shows two zones : — (1) the medullary zone, formed in greater part by 

 the epithelial strands of the first proliferation ; and (2) the cortical 

 zone, resulting from a second proliferation of the germinative epithelium. 

 In the chick, as in Mammals, the medullary strands are ephemeral for- 

 mations. They disappear a few days after hatching ; the chicken 

 fourteen days old shows no trace of them. They have a progressive 

 period of development with cellular differentiation, which gives place to 

 a counter process of regression. 



The ovary of birds is characterized by the appearance, within the 

 medullary strands, of a system of closed cavities, which have no com- 

 munication with blood-vessels or with urinary canaliculi. These medul- 

 lary cavities play a part in the process of degeneration, of which indeed 

 they are the first sign. In this process an important part is played by 

 leucocytic elements of mesenchymatous origin, which form groups in the 

 medullary zone into which they penetrate. The medullary oocytes, very 

 numerous at the end of incubation, have a brief existence. Their nuclei 

 never get past the " pachytene " stage. They are never surrounded by 

 a follicular envelope. 



The medullary strands undergo a fatty degeneration, which is particu- 

 larly marked when the constitutive cells are dis-aggregated and fall into 

 the medullary cavities, where they undergo liquefaction and absorption. 

 The more resistant gonocytes may pass from the cavities into the blood 

 stream. 



The interstitial tissue of the chick ovary appears on the twelfth day 

 of incubation. It is represented by two cellular types which differ in 

 aspect, position, and origin. The interstitial cells have a history parallel 

 to that in Mammals. There is no evidence of any trophic function of 

 the interstitial tissue in relation to the epithelial tissue. 



A constant phase in the development of the medullary strands is the 

 accumulation in their interior of fatty globules. This precedes the 

 differentiation of the medullary oocytes, and seems to be an index of a 

 transitory recrudescence of cellular metabolism. 



