STUDIES ON INSECT SPERMATOGENESIS. 77 



and determinate series of differentiations. Instead of an inert, 

 passive mass of mitochondria subject only to some enigmatic 

 structural " patterns," we find that the nebenkern is actually the 

 seat of intense activity up to a very late stage in sperm formation. 

 "What the meaning of this may be, is, however, entirely unknown 

 at present. 



A second point of very practical nature is the light thrown 

 upon the staining behavior of the mitochondria! substance during 

 spermiogenesis. It is clear that in preparations which have every 

 appearance of technical excellence, the structure of the neben- 

 kern may be seriously distorted or entirely invisible. This has 

 obviously been the cause of many incomplete accounts, and of 

 much contradiction of results even in the same animals. It now 

 becomes plain that the exact study of the nebenkern demands the 

 use of a great variety of technical methods in the hope that one 

 of them will prove adequate for the work in hand. Similarly, 

 the obvious changes in the chemical composition of the nebenkern 

 substance arouse a well-grounded skepticism as to the value of the 

 so-called " specific " stains for mitochondria. In a mass of 

 changing chemical composition such as I have shown the neben- 

 kern to be, it is manifestly impossible to talk of any " specific " 

 staining at all ; and ecmally impossible to assign a chemical com- 







position to this chondriosome body as one might to a homogeneous 

 mass. 



I have tried in this paper to put into a logical and connected 

 story the facts as we know them about the spermatid nebenkern 

 in insects. In no single form have all the features of this account 

 been, as yet, clearly made out, and my interpretation of the facts 

 as I have found them in the Hemiptera involves, therefore, a 

 large element of assumption. I have, however, felt justified in 

 these assumptions since they furnish a satisfactory basis of ex- 

 planation for all the facts so far available, many of which have 

 been entirely obscure hitherto ; and since, furthermore, they pro- 

 vide a standpoint from which a further, intelligent attack on the 

 whole problem can be made. 



By way of summary, attention may be particularly called to the 

 following points : 



