CASTLE : THE HEREDITY OF SEX. 201 



first of these polar nuclei commonly divides about at the time of forma- 

 tion of the second polar nucleus. There are thus formed three polar 

 nuclei (or cells), which all lie imbedded in the cytoplasm of the 

 egg. There regularly takes place a fusion of the inner derivative 

 of the first polar cell with the second polar cell, exactly as observed 

 by Petrunkewitsch in the case of the honey-bee. Further develop- 

 ment of this body was not observed in most of the cases studied by 

 Henking, though he mentions certain apparently abortive " attempts" at 

 division by this body. The outer product of division of the first polar 

 cell was observed regularly to undergo disintegration without further 

 change, except in a few cases, such as that of the parthenogenetic gall- 

 wasp, Rhodites rosae, in which all three polar nuclei fuse into a single 

 body. Henking seems to regard ultimate disintegration as the normal 

 fate of all the polar nuclei, whether or not conjugation has occurred 

 among them. This is precisely what the observations of Petrunke- 

 witsch would lead us to expect in the case of all fertilized eggs, as well 

 as of parthenogenetic eggs which form but one polar cell. We have no 

 reason to suppose that Henking ever studied the development of a male 

 parthenogenetic egg, in which sort alone (in addition possibly to Rhodites). 

 we should expect to find the genital gland of the embryo developing out 

 of the conjugated polar nuclei. 



If, contrary to the opinion of Petrunkewitsch, it shall be found that in 

 the male honey-bee the testis develops, not from polar cells, but from a 

 blastoraere, we may well look for evidence of segregation of the testis fund- 

 ament early in cleavage. For, if our assumption be correct, that in par- 

 thenogenetic animals the female character is uniformly dominant over the 

 male, it will be impossible for the male character to find expression in 

 the soma of the individual, until the female character has been elimi- 

 nated from it. 



(J) Special Cases. 



The explanations offered of sex-heredity in the honey-bee and rotifer 

 are applicable to all cases known to the writer of normally parthenogenetic 

 animals, except two. These are the gall-wasp Rhodites rosae, and the 

 rotifer Hydatina senta. 



A. Rhodites rosae 



In Rhodites males are very rare, and parthenogenesis is' the normal 

 method of reproduction. According to Henking, the unfertilized egg in 

 this species undergoes two maturation divisions, yet the ofispriug devel- 



