SEX-CORDS AND SPERMATOGONIA IN CHICK 385 



THE INDIFFERENT GONAD 



If the viscera are removed from the abdominal cavity of a 

 5-day chick embryo, the Wolffian bodies will be seen on the 

 posterior wall on either side of the mid-line. On the ventro- 

 medial surface of each mesonephros, beginning at the cephalad 

 extremity and extending caudad about two-thirds of the length 

 of each Wolffian body, a narrow, white, rounded ridge will be 

 observed. These narrow elongated elevations are the indiffer- 

 ent gonads. At this time they have a length of about 2 mm. 

 and there is a noficeable difference in size in favor of the left 

 gonad. 



On examining a section through the anterior portion of the 

 Wolffian body, the gonads will be seen to resemble two small 

 abrupt hillocks on the surface of the mesonephros turned 

 towards the mesentery, and, it will be noticed also that they 

 have a broad connection with the mesonephros. 



The microscope reveals, farther, that there are "three distinct 

 tissues in the gonads. 



Clothing the free surface of each genital anlagen, and extend- 

 ing for some distance over the root of the mesentery, is an epithe- 

 lium made up of two to three layers of tall columnar cells. This 

 tissue is the germinal epithelium of Bornhaupt ('67) and Wal- 

 deyer ('70) and all later investigators. This epithelium is made 

 up of columnar or rather cylindrical cells, which have oval or 

 round deep staining nuclei and possesses a distinct basement 

 membrane. This last structure is very noticeable and at this 

 stage — 5 days — can be followed over the germinal hillock as a 

 regular curved line without any irregularities of any kind. 



Under the germinal epithelium, which is thicker and more ex- 

 tensive over the left gonad, is another tissue — the stroma of the 

 gonad. This tissue is nothing but embryonic mesenchyme, and 

 as such is directly continuous with the same tissue in the Wolff- 

 ian body and in the root of the developing mesentery. The 

 cells of this tissue are loosely packed and have faintly staining 

 nuclei. The cytoplasmic part of the cells appears as indistinctly 

 bounded processes which anastomose with the processes of other 



