98 CYTOPLASMIC STRUCTURES [CH. 



that they play a predominant part in the transmission of 

 inherited characters. For this there is little evidence, and 

 it seems more probable that their main function is nutri- 

 tional, and concerned in spermatogenesis with the rapid 

 transformation of the spermatid into the spermatozoon. 

 They are usually most conspicuous in cells which are about 

 to undergo differentiation, and some workers have regarded 

 them as purely temporary structures, produced by the 

 physiological condition of the cell, perhaps as reserves of 

 nutritive material. It seems to be established, however, 

 that they have the power of division and propagation like 

 the plastids of plant cells, and with our present very im- 

 perfect knowledge it seems best to regard them as living 

 structures, of the nature of cell-organs, which may multiply 

 and become conspicuous at times when rapid intracellular 

 differentiation is about to take place. That they are inti- 

 mately associated with cell-metabolism may be inferred from 

 MONTGOMERY'S observation (1911 a) on the Hemipteran 

 Euschistus, that in the spermatogonial nucleus part of the 

 chromatin is always in contact with the membrane in one 

 area, forming a "chromatin-plate," and that although the 

 position of this plate varies, with respect to the rest of the 

 cell, in different cells, the mitochondria and "idiozome" 

 (dense protoplasm equivalent to GATENBY'S archoplasm) 

 always appear in the region of the chromatin-plate. This 

 suggests that the mitochondria arise or at least multiply in 

 connection with a process of nucleo-cytoplasmic reaction. 

 MONTGOMERY (1912) also maintains that in Peripatus the 

 whole mitochondrial body is thrown out of the spermatid 

 before its transformation into the spermatozoon is quite 

 complete, a fact impossible to harmonise with the belief 

 that mitochondria transmit hereditary characters. 



The fate of the mitochondrial body of the spermatozoon, 



