SPERMATOGENESIS OF APHIDS. 359 



The most conspicuous difference between the smaller sperma- 

 tids of the honey bee and this aphid is seen in the nuclei. The 

 nucleus of the smaller spermatid of the honey bee returns to a 

 resting stage, and differentiates similar to that of the larger 

 spermatid. The nucleus of the smaller spermatid of this aphid, 

 however, becomes condensed after the second spermatocyte divi- 

 sion, and remains in the same state, although the cytoplasm shows 

 changes similar to those of the larger spermatid. This may be 

 caused by the absence of the lagging chromosomes in the smaller 

 spermatids, while in the honey bee the smaller spermatids have 

 the same number of chromosomes as the larger spermatids. 



Whitney (1918) mentions that the normal and rudimentary 

 spermatozoa have been found in considerable number of rotifers. 

 In his paper of 1917 he says that the functional spermatozoa are 

 identical in their power of determining the sex of the individual 

 that develops from a fertilized egg, since after a functional sper- 

 matozoon has fertilized a parthenogenic male egg, the egg always 

 develops into a female individual. 



In the case of these rotifers, according to Whitney, the chro- 

 mosomes divide in the first spermatocyte division. One half of 

 the secondary spermatocytes divide and form the normal sper- 

 matids. The remaining half of the secondary spermatocytes, 

 contrary to the case of the smaller secondary spermatocyte of 

 Stomaphis yanois, do not divide, but develop directly into the 

 degenerate spermatozoa. The spermatocytes destined to degen- 

 erate are smaller than the others, and their development into the 

 complete rudimentary spermatozoa is strikingly different from 

 the development of the normal spermatids. 



Whitney ('18) says that as all the fertilized eggs in both phyl- 

 loxerans and rotifers develop into female young, it seems safe to 

 conclude, as Morgan has already concluded, that the degenerate 

 sperm cells are the male-determining ones and that the normal 

 sperm cells are the female-determining ones. 



Stevens (1905) found many degenerate spermatozoa in Blat- 

 tella germanlca. She states that the distribution and varying 

 number of these degenerate spermatozoa make it impossible to 

 interpret their condition as due to the absence of the accessory 

 chromosome as Miss Wallace does in the spider, and that the only 



