The Germ Cells of Aphis. 325 



In Rhodites rosie (Henking) there are two maturation divisions 

 but no reduction of chromosomes in eggs that produce females. 

 Males are rare and the maturation of the male egg is not known. 

 In Artemia salina (Brauer, '94) either one polar body only is 

 formed, or a second division occurs and the resulting nucleus con- 

 jugates with the egg nucleus. Here again the female and male 

 generations seem not to have been distinguished. 



Weismann and Ischikawa ('88) found onlv one polar body in 

 the parthenogenetic eggs of several rotifers and crustaceans, no 

 statement being made in regard to the male generations. Mrazek 

 ('97), and Erlanger and Lauterborn ('97) found that in Asplanchna, 

 a rotifer, the parthenogenetic female eggs gave off one polar body, 

 while the parthenogentic male eggs formed two, and there was 

 no indication of a union of the second polar body with the egg 

 nucleus. 



In Hydatina senta (Lenssen, '98) the first maturation division 

 in parthenogenetic female eggs goes only as far as the metaphase; 

 there is no reduction, and the chromosomes (10 or 12) fuse to form 

 the egg nucleus. In the male egg reduction occurs, 5 or 6 chro- 

 mosomes appearing in the polar plates of the spindle. In Hyda- 

 tina it is supposed that the first maturation division is suppressed 

 in both the parthenogenetic and the sexual eggs. In the Aphid 

 only one polar body is given off in the parthenogenetic egg — ^^male 

 or female — and there is no evidence of reduction in either male 

 or female parthenogenetic egg. 



Thus we find a series, beginning with forms where partheno- 

 genesis is either occasional or continues for onlv one generation, 

 when maturation appears to follow the usual course for fertilized 

 eggs; and ending with Hydatina senta where the whole process is 

 practically suppressed in the parthenogenetic female eggs, and the 

 Aphid where one maturation division without reduction remains 

 in both male and female parthenogenetic eggs. We are thus led 

 to question the importance of the second polar body in deter- 

 mining the male sex, also to question the view that parthenogenesis 

 is due to the suppression of one or both maturation divisions, and 

 to suggest that the various degrees of suppression of maturation 

 phenomena in parthenogenetic eggs may be a more or less simple 

 and perfect adaptation to a necessity of continued parthenogenetic 

 reproduction, i. e., the retention of the full double series of mater- 

 nal and paternal chromosomes throughout the parthenogenetic 



