426 ELMER L. SHAFFER. 



of the spermatocytes are genetically related to the granular 

 ones of the spermatogonia. There is no evidence that the 

 mitochondria go through a process of pairing during the growth 

 stages; on the contrary they increase in numbers. This increase 

 in the numbers of the mitochondria is a most important point 

 in an understanding of their nature and significance. Such an 

 increase in numbers of mitochondria during the growth period 

 has been explained by some workers (Goldschmidt, Buchner, 

 etc.) as being due to an elimination of material from the nucleus 

 into the cytoplasm (chromidial theory). On the other hand, 

 another group of workers insist that mitochondria are always 

 derived from pre-existing mitochondria by a process of autonom- 

 ous division. Wilke ('13) has described such a process in 

 Hydrometra. As will be shown later, it is quite possible that 

 the mitochondria may arise in another way. 



As the first maturation spindle is forming (Fig. 21), the mito- 

 condria begin to migrate from one pole of the spindle towards 

 the opposite pole and finally surround the entire spindle by 

 the time of the metaphase (Fig. 22). As the chromosomes begin 

 to divide in the anaphase, there is no indication of any division 

 of the mitochondria (Fig. 25). In the late anaphase, when the 

 cell-constriction begins to appear (Fig. 27), the mitochondria 

 begin to divide, so that when the cell-constriction is complete, 

 the daughter cells (second spermatocytes) each contain approxi- 

 mately equal amounts of mitochondria (Fig. 28). The view of 

 autonomous division is not supported here and it is quite evident 

 that their division is due to their separation by the cell-con- 

 striction. 



In the second maturation division, the behavior of the mito- 

 chondria is the same as in the first maturation division ; they 

 surround the spindle peripherally and become divided by the 

 cell constriction (Fig. 29), so that the daughter cells (spermatids) 

 receive equal amounts of mitochondria. As is usual in the 

 insects, the mitochondria of the spermatid become resolved into 

 a compact body, the Nebenkern (Fig. 30, N), which usually 

 shows a lighter peripheral area. It is interesting to note that 



There are many other cases in which the mitochondria are not localized at one 

 pole of the nucleus in the spermatocyte, and while such localization is common, 

 it is not general as Duesberg maintains. 



