kellogg] GALLS AXD GALL-FLIES 113 



subject to the greatest modification and many small fibro-va^cular 

 bundles form in this modified mesophyll. Both Adler and Sockeu 

 consider that after the first stages of formation the gall becomes an 

 independent organism growing upon the host-plant. Cook believes 

 this to be true of the Cynipid galls. A surprising conclusion arrived 

 at by Cook is that the morphological character of the gall depends 

 upon the genus of the insect producing it rather than upon the 

 plant on which it is produced ; i. <?., galls produced by insects of a 

 particular genus show great similarity of structure even though on 

 plants widely separated ; while galls on a particular genus of plants 

 and produced by insects of different genera show great differences. 

 The formation of the gall is probably an effort on the part of the 

 plant to protect itself from an injury which is not sufficient to cause 

 death. 



An additional interesting feature in the economy of Cynipid life is 

 the presence in the galls of other insects besides the gall-makers. 

 These others are on two footings, that is, some are guests or com- 

 mensals, and some are true parasites, either on the gall-makers or on 

 the guests. Curiously, among both guests and parasites are members 

 of the same family, Cynipidae, to which the makers and rightful 

 owners of the galls belong. Others of the parasites may belong to 

 the various well-known parasitic hymenopterous families, as the Ich- 

 neumonidse, etc., while others of the commensals may belong to 

 entirely distinct orders, as the Coleoptera [beetles], Lepidoptera 

 [butterflies], etc. Kieffer (a famous French student of galls and 

 gall-flies) gives the following amazingly large list of commensals and 

 parasites bred from a common root-gall on oak. Commensals, the 

 larvae of five species of moths, of one fly, of one beetle, of one Neu- 

 ropteron, and of two Cynipids ; parasites, a total of 41 species, bred 

 mostly from the various commensals. 



The guest gall-flies, called iniquilines, are often surprisingly sim- 

 ilar to the species which actually produces the gall. A similar like- 

 ness between host and guest exists in the case of the bumble-bee 

 (Bombusj and its guest Psithyrus (closely related to Bombus*. It 

 may be that the guest species is a degenerate loafing scion of the work- 

 ing stock. 



The group of gall-flies and their allies is looked on as a super- 

 family, the Cynipoidre, in the latest authoritative classification (Ash- 

 mead) of the Hymenoptera, and divided into sub-families, the 

 Cynipoidae including the gall-makers, and the much smaller family, 



