408 CHARLES H. SWIFT 



Wolffian body. When the embryo is 11 days old the stroma 

 begins to increase in quantity and the seminiferous cords com- 

 mence to meander and to anastomose with each other. 



5. Up to the thirteenth day of development the primordial 

 germ-cells in the sexual cords do not divide, their numbers re- 

 maining about the same as when they left the germinal epithe- 

 lium. Beginning at this stage they divide actively and continue 

 to do so for the next four daj'^s. The primordial germ-cells 

 give rise to the spermatogonia, which are from now on very 

 numerous in the sexual cords. The spermatogonia differ from 

 the primordial germ-cells in possessing the mitochondrial cres- 

 cent. This occupies part of the vegetative pole and consists of 

 attraction-sphere containing centrosomes, and mitochondria, 

 which in section are seen to extend over the nuclear mem- 

 brane, capping the nucleus. The arms of the mitochondrial 

 body may embrace more than one-half of the nucleus. This 

 mitochondrial body is suspended in dense cytoplasm and is 

 exactly comparable to the yolk nucleus as described by D'Hol- 

 lander and Van der Stricht in the oocyte. I have also described 

 it in the young oogonia of the chick. The interstitial cells 

 appear in the stroma on the thirteenth day but reach their 

 greatest development during the seventeenth day. They are 

 simply differentiated stroma cells, since they do not divide and 

 transitional forms can be seen. 



6. Cavities begin to appear in the network of seminiferous 

 cords during the twentieth day. These cavities are formed, not 

 by fissures between the cells, but by Uquefaction of the cells in 

 the central axis of the cord. At the twentieth day the sperma- 

 togonia are found against the basement membrane, with the 

 nucleus towards the central axis of the cord and the mitochon- 

 drial crescent near the basement membrane. They probably 

 reach this position by amoeboid migration. The elongated 

 cells between the spermatogonia are derived from the peritoneal 

 cells of the seminiferous cords. 



7. The primordial germ-cells give rise to the spermatogonia 

 and the coelomic cells of the germinal epithelium produce the 

 supporting cells of the seminiferous tubule. 



