416 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- 
