406 ELMER L. SHAFFER. 



mitochondria constitute the idioplasm is an entirely different 

 problem. Modern researches in genetics have shown that, 

 despite mutations, hereditary characters are relatively stable 

 and that the hereditary constitutions of organisms are definitely 

 organized; hence the idioplasm which is causal in the develop- 

 ment of the hereditary characters must similarly be stable and 

 highly organized. 



Keeping in mind the "cell as a whole," I have studied the 

 chromosomes and mitochondria in the oogenesis and spermato- 

 genesis of Cicada, and my observations give added evidence to 

 the chromosomes as the idioplasmic substance, while there is no 

 evidence from an unbiased standpoint that the mitochondria 

 behave as idioplasmic substances. There is evidence, however, 

 that the mitochondria are intimately concerned in cell meta- 

 bolism. 



Throughout this work I have had the constant advice and 

 encouragement of Prof. E. G. Conklin, and it is with great 

 pleasure that I here express my indebtedness. 



B. MATERIALS AND METHODS. 



The youngest specimens of Cicada obtained were those of the 

 second pupal stage about three weeks prior to their emergence 

 from the ground and their final moult into the imago. These 

 specimens were collected about the middle of April by digging 

 under trees in the vicinity of Princeton. The pupae were found 

 lying about a foot from the surface of the ground and were most 

 abundant several feet away from the tree trunks. In the testes 

 of such pupae, one finds most of the cells in the maturation stages 

 besides an abundance of spermatids, spermatozoa, and a few 

 spermatogonia. In the adult or imago, the testes are almost 

 completely filled with sperm except for a small number of 

 spermatogonia. After copulation, the testes are reduced to about 

 one tenth their former size and contain only a small residue of 

 spermatozoa, some degenerated cells and a few spermatogonia 

 which also show signs of degeneration. 



There are two testes, each consisting of a great many radiating 

 ellipsoidal follicles which give the testes a berry-like appearance. 

 In the female there are two typical ovaries, each consisting of a 



