THEORIES OF GALL ORIGIN. 23 



the venom of gall-flies and wasps is different, it being 

 in the latter for defence or offence against other 

 insects. Apart from strength of virulence, it may 

 also be stated that there is a chemical difference in 

 some wasp venom, as is shown by some of them 

 being more alkaline, in contradistinction to the usual 

 acid nature of most species. But, as regards the 

 Cynipidse secretion, we have no evidence of any 

 chemical or molecular difference ; while the analogy to 

 contagia is hardly applicable, since these are living 

 organisms which cause changes in the animal system 

 by their growth and multiplication. The only infor- 

 mation we have of the nature of the gall-fly venom 

 is that given by Beyerinck,* who describes it as 

 tasteless and smell-less, and as a substance which, 

 when injected into the hand, produces no ill effect 

 whatever, while the poison of wasps does so when 

 injected in the same way ; and, finally, we know from 

 direct observation that its use is to close the hole 

 made by the ovipositor when the eggs are laid. Again, 

 Paszlavsky (Terms. Fuzetek, v) states that he has 

 seen Bhodites rosse give out during oviposition a 

 transparent fluid clear as water, which flowed over the 

 branchlets and leaflets. Even in the Tenthredinidse, 

 where larval irritation can have nothing to do with 

 the growth of the gall, apparently one of its uses is to 

 keep the wound made by the saw for the reception of 

 the eggs from closing in and crushing them. 



So far, therefore, as regards the Cynipidse we may 

 conclude (1) that there is no evidence that the venom 

 has anything to do with the origin of the gall, — 

 on the other hand, there is every reason to believe 

 that its use is to close the wound ; and (2) that as 

 observation shows that the mechanical irritation pro- 

 duced by the birth and growth of the larva is the 

 primary factor in gall genesis, we may fairly conclude 

 that the theory of mechanical irritation is more in 

 consonance with observed facts than the infection one. 



■* Ueber d. ersten Entwick. einiger Cynipidengallen, p. 179. 



