282 FRANZ SCHRADER 
optera the sexual eggs normally undergo two maturation divi- 
sions, in the course of which the chromosome number is halved. 
As in ease of Trialeurodes vaporariorum, such eggs will develop 
into males if unfertilized, but if the diploid number is restored 
through the entrance of a spermatozoon, a female is developed. 
Although haploid parthenogenesis of the sexual eggs thus 
appears to be normal among Hymenoptera, there appear to be 
cases where certain eggs are asexual, parthenogenetic develop- 
ment taking place with the complete diploid number of chromo- 
somes. As might be expected, such eggs give rise to females. 
This is found most generally in species where there is an alter- 
nation of sexual and parthenogenetic generations. I need men- 
tion only the gall-fly, Neuroterus lenticularis (Doncaster, ’10, 
’11, 716), where the spring generation consists solely of partheno- 
genetic females, while the summer generation is represented by 
males and sexual females. The eggs of the latter undergo matu- 
ration and reduction like those of ordinary Hymenoptera, and 
since these eggs must be fertilized in order to develop, they always 
give rise to females (the parthenogenetic females mentioned 
above). The parthenogenetic females, however, produce two 
types of eggs. Those which give rise to the males again conform 
to the normal in that reduction takes place and parthenogenesis 
is haploid, while in those eggs from which females are developed, 
the diploid number is retained. Doncaster believes that there 
no polar bodies are given off. These proceedings are thus ap- 
parently clear, but what seems to be a more exceptional case is 
furnished by Rhodites rosae. No males have been found in this 
species by cytological investigators, and parthenogenesis is with- 
out doubt obligatory. Judging from analogous cases, it might 
be expected that such parthenogenesis is diploid, but analysis 
of the case presents various difficulties. Henking (’92) and 
Schleip (’09), both of whom have investigated maturation in 
these eggs, agree that two polar bodies are given off. Henking 
regards meiosis as normal, the chromosomes being reduced to the 
haploid number. The diploid number is, however, then restored 
in the first cleavage through a doubling of each chromosome. 
