132 GERM-CELL CYCLE IN ANIMALS 



rod, the other half do not. Of the forty-nine penul- 

 timate spermatogonia examined, twenty-four ex- 

 hibited a rod and twenty-five did not. This result 

 has been confirmed by von Winiwarter. When the 

 rod-containing penultimate spermatogonia divide, 

 there is a similar segregation of the rod in one of 

 the daughter cells, hence only one-fourth of the cells 

 resulting from the divisions of the antepenultimate 

 spermatogonia possess a rod. Of one hundred 

 and forty-two cells of this generation studied by 

 Montgomery, twenty-five were found with a rod and 

 one hundred and seventeen without. That this 

 ratio is less than one to three (1:3) is explained by 

 the fact that some of the spermatogonia with rods 

 may already have become Sertoli cells. The further 

 history of the rod in the Sertoli cell is as follows : A 

 primary rodlet is produced by a splitting of the rod 

 (Fig. 41, C) after which the rod either disappears 

 at once or else persists for a time, in which case it 

 may split longitudinally as shown in Fig. 41, D. 

 However, in four-fifths of the cells examined (one 

 hundred in number) the large rod disappeared 

 before the growth of the Sertoli cell had begun. 

 Each primary rodlet splits longitudinally into two 

 approximately equal parts, called secondary rodlets 

 (Fig. 41, D, rz), which persist until the end of the 

 cycle of the Sertoli cell. 



Neither Montgomery nor von Winiwarter were 

 able to determine the origin of the rod. They do 

 not consider it mitochondria! in nature, although 

 it may arise from granules lying in the cytoplasm. 



