SPERMATOGENESIS OF LEPISMA DOMESTICA 401 



Mitochondria 



Mitochondrial structures are present in the spermatogonia, 

 but in verj^ small numbers, and it is difficult to make them out. 

 At the beginning of the growth period they appear clearly as a 

 dark-staining crescent-shaped mass usually located at one end 

 of the cell. This mass soon breaks up and forms some six to 

 eight bodies differing from each other in shape and size (fig. 21), 

 but retaining an almost constant number. These bodies take the 

 stain intensely and appear as the most prominent structures 

 during the entire growth period. As the cell increases in size, 

 the mitochondria becomes so conspicuous, even by ordinary 

 iron-haematoxylin staining, that the cytoplasm seems like a 

 dark border about the nucleus, and in this dark-staining mito- 

 chondrial matrix the clumps stand out clearly. 



During the first maturation division the ring of granular 

 mitochondria encircles the entire spindle, while the larger bodies 

 are scattered about the cytoplasm and are located near but not 

 on the spindle. The mitochondrial material seems to divide 

 equally, half the granular material as well as four clumps going 

 to each cell (fig. 39). In the resting stage of the second sperma- 

 tocyte the mitochondria forms a narrow dark-staining ring 

 about the nucleus, but the clumps are no longer apparent (figs. 

 49, 50, and 51). In figure 54 the granular mass is seen arranged 

 about the spindle of the second division, while figure 61 indicates 

 how they gather about the chromatin at the poles of the young 

 spermatids. In the description of the spermatids the further 

 history of the mitochondria has already been given. 



DISCUSSION 



The resting stage 



While in many animals no resting nucleus is formed following 

 the first maturation division, the chromosomes of the telophase 

 being quickly transformed into the prophases of the second 

 division, there are quite a number of exceptions reported in the 

 literature. 



