1864.] 549 



about these inquilinous insects, whicli have true gall-makers closely 

 allied to them, is that they do not invariably confine themselves to the 

 galls of their allies, but occasionally inhabit galls made by insects that 

 even belong to different Orders. For example, the Cecidomyidous 

 gall Q. pilulse Walsh, as was just now stated, is inhabited by a Cyni- 

 pide, Ceroptres* (amblynotus) inermis Walsh, and conversely from the 

 Cynipidous gall Q. petiliocoJa 0. S., I bred July 11th two specimens of 

 a Lasioptera (^Cecidomyidae) resembling somewhat L. solidaginis 0. S. 

 but perfectly distinct from that species. Again, numerous instances 

 are given in this Paper, where Saw-flies are inquilinous in the galls of 

 Gall-gnats, and Gall-gnats are inquilinous in the galls of Saw-flies, as 

 may be readily seen from the lists of Inquilines under Diptera and 

 Hymenoptera. But in all such cases this appears to be the exception 

 and not the rule. It should be remembered, that the same gall is often 

 inhabited by several different species of inquilines, sometimes belong- 

 ing to widely distinct groups, as, for example, the Cynipidous gall Q. 

 petlolirola 0. S. is inhabited not only by the Guest Gall-gnat mentioned 

 above, but by a Guest Gall-fly, Ceroptres (^amhlynotus) petioh'cola O.S.; 

 (Froc. Ent. Soc. Phil. T. p. 67 and II. p. 487,) and that many species 

 of these Guests habitually live in the galls of several different species 

 of Hosts, many instances of which will be found below. It is even 

 occasionally the case, that one and the same species is sometimes inquili- 

 nous in the galls of other insects, and sometimes attacks natural sub- 

 stances which are in nowise connected with galls, of which one in- 

 stance is apparently found in the Dipterous Drosoplula cmioena Lw., 

 and another notable one occurs in the common Curculio {Conotrache- 

 Ivs ne7iuj}har Hbst.), one brood of which attacks the fleshy part of the 

 Plum, Peach, &c., and another brood habitually lives in what will be 

 shown below, to be in all probability a true Cecidomyidous gall — the 

 well-known " Black-knot" on the Plum-tree. (See under No. 15.) 



Nothing gives us a better idea of the prodigious exuberance of Insect 

 Life, and of the manner in which one insect is often dependent upon 

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



* Baron Osten Sacken tells me that he has learned from Dr. Eheiuhardt of 

 Germany, that the insects provisionally referrel by him to Hartig's imper- 

 fectly defined genus Amblynotus belong in reality to Hartig's genus Ceroptres, 

 or at all events must form a new genus closely allied to Ceroptres. 



