THE ORGANS OP THE MIDDLE GERM-LAYER. 



383 



follicle-like structures become hollow and thus converted into seminal 

 ampullce, whose epithelial cells gradually grow out into long cylinders. 

 The greater part of these become seminal mother-cells, which by 

 many repeated divisions are converted into sixty seminal cells, each 

 of which is metamorphosed into a seminal filament. Since the 

 filaments derived from each 

 seminal mother-cell always 

 arrange themselves parallel 

 to one another, it is easily 

 understood why before the 

 attainment of complete 

 maturity the seminal fila- 

 ments are found united in 

 great numbers into bundles. 

 Whereas the testis, Uhe 

 the ovary, draws its specific 

 histological components di- 

 rectly from the germinal 

 epitheliwm, it acquires its 

 afferent ducts from, tlie 

 primitive kidney. As in 

 the female; so also in the 

 male, epithelial shoots, the 

 sexual cords (genital canals 

 of Hoffmakn), grow from 

 the primitive kidney to- 

 ward the testis ; in the 

 Amphibia they arise as 

 proliferations from the 

 cells of the wall of certain 

 Malpighian corpuscles; in 

 the Selachians, on the con- 

 trary, they sprout out in a 

 somewhat different manner 

 from the cUiate funnels. 



Arrived at the base of the testicular ridge, they are joined together 

 into a longitudinal canal, from which fine tubules are sent stUl 

 farther into the substance of the testis, where they unite with the 

 structures that take their origin in the germinal epithelium. As 

 figure 218 B shows, the eiFerent tubules (sc), in Selachians at 

 first apply their blind ends to the ampullae, and enter into open 



