PARTHENOGENESIS. 25 



Parthenogenesis. 



With regard to the relative number of the two sexes, 

 it is only with a few species that the males and 

 females can be said to be in anything like equal 

 numbers. As a rule the males are far fewer than the 

 females, and this remark holds good not only with 

 captured specimens, but also with those bred. Not 

 only are the males fewer, but with some species they 

 are absolutely unknown, while with several species 

 which have males in tolerable numbers parthenogenesis 

 plays a normal or occasional role. 



Of common species provided with males, but in 

 extremely limited numbers compared with the females, 

 may be mentioned Strongylogaster cingulatus, Selandria 

 stramineipes, Hemichroa aim, Croesus varus, Blenno- 

 campa ephippium, Eriocampa adumbrata, Nematus 

 qucrcus, N. gallicola, N. acuminatus. Of Stron. cingu- 

 latus, Mr. Frederick Smith wrote me that he had only 

 taken in all five or six males, and these not on the ferns, 

 but on UmbellifercB in company of the females ; while 

 often he had had forty or fifty females in his net at one 

 time without a single male. My own experience with 

 this species is exactly the same. The only male I have 

 taken of 8. cingidatus was bred, and curiously enough it 

 appeared a fortnight after the females. I have often 

 reared N. gallicola, but have never been able to pro- 

 cure a male ; Mr. Smith has been more fortunate, 

 although even with him there only occurred " a single 

 male out of several hundreds of the flies " (Proc. Ent. 

 Soc. Lond., pt. iii, 1876, p. 22). Croesus varus is only 

 known to have a male from the very doubtful account 

 of its original describer Villaret, and that of Blenno- 

 camp a ephippium from a single specimen taken by 

 Brischke (Beitr. zur Parth. d. Arth., p. 228). The 

 male of Eriocampa adumbrata is very scarce, and I have 

 only seen one myself. As an example of a species 

 where the males may be said to be tolerably common 



