498 HYMENOPTERA 



of generations. Thus in Rhodites rosae the generations resemble 

 one another, and the male is very rare, but is still occasionally 

 produced, 1 and the same condition exists in other Cynipidae. 

 According to the observations of Adler, we may assume that the 

 male, in the latter cases, is useless, the continuation of the species 

 being effected by virgin females although males exist. Deutero- 

 kous parthenogenesis also occurs in the sawflies, but as a com- 

 paratively rare phenomenon. 2 



Thelyotokous parthenogenesis is common in sawflies, and it 

 also occurs in some Cynipidae. There are several species of this 

 latter family in which no males have ever been found. 3 The 

 phenomena in Rhodites rosae we have mentioned, give rise to 

 the idea that in that species deuterotokous parthenogenesis occurs 

 as an exception, the species being usually thelyotokous. A 

 most remarkable case of thelyotokous parthenogenesis is said to 

 exist in the case of the parasitic ant Tomognathus. This species 

 is said to be monomorphic, only the female existing, and repro- 

 ducing by uninterrupted parthenogenesis. 



Arrhenotokous parthenogenesis i.e. parthenogenesis in which 

 the progeny is entirely of the male sex occurs in several species 

 of sawflies. We find it also occurring in the case of the social 

 Hymenoptera ; the workers of ants, bees, and wasps occasionally 

 produce eggs parthenogenetically, and the progeny in these 

 cases is always of the male sex. In the honey-bee the queen 

 sometimes produces eggs before she has been fertilised, and 

 the parthenogenetic young are then always of the male sex. 



Some species of Hymenoptera exhibit two forms of partheno- 

 genesis. In Nematus curtispina the parthenogenetic generation is 

 generally of the male sex, but a female is occasionally produced ; 4 

 while in Hemichroa rufa parthenogenesis may result in either 

 deuterotokous or thelyotokous progeny. No case is yet known 

 of a species exhibiting the three forms of parthenogenesis. From 

 this review we may conclude that parthenogenesis does not 

 favour the formation of one sex more than another ; but it is 

 clear that it decidedly favours the production of a brood that is 



1 Adler, Deutsche ent. Zeitschr. xxi. 1877, p. 209. 



2 Cameron, Brit. Phyt. Hym. Ray Society, i. 1882, p. 29, and ii. 1885, p. 218. 



3 Cameron, op. cit. iv. 1893, p. 9. 



4 Brit. Phyt. Hym. i. p. 27. Fletcher's record, referred to by Cameron, men- 

 tions N. miliaris, but this name was probably erroneous. 



