1864.] 547 



occasionally inhabit these galls, there are of true Inquilines which seem 

 to inhabit them exclusively, but without always confining themselves to 

 one particular species of gall, seven cecidomyidous species, two tenthre- 

 dinidous species, and at least one and probably four or five Coleoptera, 

 besides seven species of Microlepidoptera, which Dr. Clemens has kindly 

 undertaken to name and describe from specimens with which I have 

 furnished him. Each of the above, with the exception of the last, will 

 be noticed below under the head of the Order to which it belongs. 



From the great number of these Inquilines, it must be obvious that 

 there is considerable dano;er of mistakino- them for the true authors of 

 the gall. For example, any one who examines the Tenthredinidous gall 

 *S'. pomum n sp. in the middle of the summer, will find nearly half of 

 them to contain Anthonomus scuteUatus Schonh. either in the larva, 

 pupa or imago state, unaccompanied by any Tenthredinidous larva ; 

 whence, as I myself formerly did, he would be very likely to jump to 

 the conclusion that it was that insect that made the gall. A more ex- 

 tensive knowledge, however, of the galls of the willow will soon show 

 him, that this same beetle occurs in great numbers in several other 

 galls, some of them of a totally difi"erent structure ; and hence he will 

 properly infer that the same insect cannot make two totally different 

 kinds of gall, and consequently that it must be a mere inquiline in 

 S. pomum. There is another criterion which will be found very useful 

 in determining the question, which of two insects bred from a given 

 gall is the true Gall-maker and which the Inquiline. In all monotha- 

 lamous galls, whether Cecidomyidous or Cynipidous, there is always a 

 centi'al cell or nucleus, in which the gall-maker resides, the inquilines 

 either residing outside the central cell, or, as I believe to be often the 

 case, and as must be the case with the Snout-beetle just now referred 

 to, destroying the tenant of the central cell and occupying his place. 

 If then non-parasitic pupae taken from the central cell of a gall are 

 isolated in one vial, and non-parasitic pupa? taken from outside the 

 central cell are isolated in another vial, and the former always produce the 

 imago A, and the latter always produce the imago B, it must be evident 

 that A is in all probability the gall-maker and B beyond all doubt an 

 inquiline. In this manner I ascertained that the pine-cone like gall 

 S. strohiloides 0. S. is not made by the cecidomyidous larva, which 

 was observed by Osten Sacken to live in great numbers under the 



