THE ENTOMOLOGIST. 241 



Society of Philadelphia for 1864. In this paper the author 

 proposed to name and describe the galls found on willows at 

 Rock Island, Illinois, the insects which produce thevn, and 

 also other insects which habitually breed in the galis formed 

 by true gall- makers, and which, as they feed on the sub- 

 stance ottlie gall itself, and only occasionally or incidentally 

 destroy the gall-making insect, may be appropriately con- 

 sidered as " luqnilines" or Guest-flies. Mr. Walsh enume- 

 rates five species of willow — iSalix discolor, MuIiL, which 

 fields three distinct galls ; S. cordata, MuJd., which yields 

 six galls ; S. longifolia, Miihl., which yields three ; S. nigra, 

 Mais/iall, which yields two galls ; and S. humilis, Morsltallj 

 which yields no less than ten distinct galls ; some of these 

 galls, however, occur on more than one species of willow. 

 Besides the true galls, a Coleopterous pseudo-gall was found 

 on Salix longifolia. Of twenty-one undoubtedly distinct 

 galls, twelve are made by Diptera (CecidomyicUe) and six by 

 Hymenoptera (Tenthreaiuidje). In addition to a great num- 

 ber of insects which occasionally inhabit these galls, there 

 are, of true inquilines, which seem to inhabit them ex- 

 clusively, but without confining themselves to one particular 

 species of gall, seven Cecidoniyidous species, two Teuthredi- 

 nidous species, and at least one, and probably four or five, 

 Coleoptera, besides seven species of Micro -Lepidoptera. 

 The author points out the danger of mistaking inquilines for 

 the true makers of the gall, and gives numerous instances in 

 which sawflies are inquilinous in the galls of gall-gnats, and 

 gall-gnats inquilinous in the galls of sawflies. The same 

 gall is often inhabited by several different species of inqui- 

 lines, and many species of guests habitually live in the galls 

 of several different species of hosts. Occasionally one and 

 the same species is sometimes inquilinous in the galls of 

 other insects, and sometimes attacks natural substances in no 

 wise connected with galls. " Nothing gives us a better idea 

 of the prodigious exuberance of insect life, and of the man- 

 ner in which one insect is often dependent upon another for 

 its very existence, than to count up the species which haunt, 

 either habitually or occasionally, one of these willow-galls, 

 and live either upon the substance of the gall itself or upon 

 the bodies of others insects that live upon the substance of 

 the gall. In the single gall, Salicis brassicoides, n.sp., there 



