4i 6 Experimental Zoology 



and, being retained, brings about self-fertilization. Blochmann 

 showed, however, in the honey bee, that two polar bodies are 

 thrown out from the drone eggs, yet they develop without fer- 

 tilization. In the rotifer Asplanchna, it has been shown by 

 Erlanger and Lauterborn that while the female parthenogenetic 

 egg gives off only one polar body, the male egg gives off two. 

 These facts show that there is no universal rule in regard to the 

 number of polar bodies that are extruded by parthenogenetic 

 eggs. Furthermore, the fact that in hermaphrodite animals two 

 polar bodies are always extruded also shows that the problem of 

 sex determination is not necessarily connected with this process. 

 It would be erroneous, however, to conclude from these cases that 

 the retention of one polar body may not in certain species be a 

 possible factor in sex determination, although not necessarily 

 because of the retention of male or of female elements. 



Since half the inherited chromosomes are supposed to be given 

 off in one or the other polar body, the question arises whether 

 this happens in parthenogenetic eggs in those cases where a 

 single polar body is produced. In the case of the aphids, Stevens 

 has shown that in the division that leads to the formation of the 

 single polar body of the parthenogenetic cycle, the full number of 

 chromosomes is present, and the division of the chromatin is an 

 equation division. There has been no pairing of the chromo- 

 somes to give the reduced number, preparatory to the polar body 

 division, as in sexual eggs. Hence the full number of chromo- 

 somes is present in the polar spindle. I have obtained the same 

 result in phylloxera ; both in the eggs that do not make the sexual 

 forms, and in the male and female producing eggs also. Since 

 the latter produce either male or female individuals, it seems 

 unlikely in these cases, and probably by inference in fertilized 

 eggs also, that the determination of sex is necessarily connected 

 with this division. 



At the second or differential division when the other polar body 

 is formed, it is supposed that only the maternal and paternal 

 (united) chromosomes separate. There is nothing, therefore, 

 in this process to suggest that it is connected with sex differentia- 



