THE .liAEERICAN ENTOMOLOGIST. 



107 



two small specimens of thi* ^all growing upon 

 (he cane of the wild Frost Grape in Illinois; and 

 we were presented w-ith two very large speci- 

 mens by Mr. Mills of Hocli Islimd, 111., which 

 had grown upon a Frost Grape planted in his 

 dooryard, from one of which the annexed draw- 

 ing is copied (Fig. 80). Tlie whole nui~s of 

 galls springs from a common ceniii' 

 [Fig. si;.! 



where a bud would normally be, ami is evi- 

 dently a mere deformution of a bud. Occasion- 

 ally an uudeformed leaf witli its peduncle still 

 entire puts forth from the common centre, some- 

 times bearing a couple of galls at the junction 

 of the peduncle with the loaf. Each gall is one- 

 celled, the cell being about a quarter of an inch 

 long and one-fourth as wide as long, and con- 

 taining a single larva. (Sec Fig. 86,6). Tlic 

 larva closely resembles that of the (Trapc-viiie 

 Apple-gall, and is tiierefore no doubt tliat of 

 some Gall-gnat. Large sized specimens of this 

 gall bear a general resemblance to a bunch of 

 lilbert or hazel nuts, as they grow on the bush: 

 hence the name that we have given it. Vnller 

 details will be found in the foot-note.* 



of from 10 to .50 opaque, woolv-pubescent. fusifonn, or 

 sometimes nattish-oval, Ki-een Rail*, lach from 30 to O.V.'i 

 inch long, the whole springinu- lr..in the |i..iiit n here normal- 

 ly a bull wouhl he l.ieate.l . IJriiiriilh il i-onlv the terniiual 

 Jof each sail that i- imlieseeni. i;e- lia-al ', iicin;.' smooth. 

 The interior of each Rail Ulle^hi , iiii.-v ;ni.t -ui.a.-hl, with a 

 Erie longituilinally eentral eell n.i". iie-li l"n':; and n.iji; inch 



(Jails made by Plant-lice (Aphid(c]. 

 The galls hitherto referred to have been those 

 whicli arc formed by the mother insect depositing 

 one or more eggs in or on the tissues of the plant 

 which she infests. Those to be now treated of 

 belong to the second or exceptional group, 

 which are formed by a young larva stationing 

 itself externally upon some particular part of the 

 infested plant, usually the leaf, and causing that 

 part to bulge out into a sack, which finally closes 

 at its mouth and shuts up the larva in a kind of 

 prison of its own making. "We see the abortive 

 beginnings of this process in the case of many 

 species of Plant-lice and of Mites ; for example 

 the common Currant Plant-louse {Aphis ribis) , 

 and sundry Mites that attack tlie leaves of oaks. 

 For here, although the leaf bulges out into a ca- 

 pacious lioUow inhabited by the leaf-feeders, yet 

 the Iiollow never, under any circumstances, 

 closes at its mouth into a true sack-like gall. 



i^ 



LiARVA. — Uranpe-venov 

 paler Breast-bone as 

 U inch. 



\i;(jNi) (tai.i. {Fopitli vayabunda, 

 Walsh), Fig. 87.— This gall occurs iu particular 

 years in prodigious abundance on the tips of the 

 twigs of certain Cottonwoods, but in other 

 years tlicre is not one to be found in the same 

 district. The old blackened galls, however, 

 hang on to the twigs for several seasons, giving 

 the tree a singular appearance when tlie leaves 

 are off in the winter time. The fly was discov- 

 ered and described before it was known to in- 

 habit any gall, and received its name from the 

 habit that it has of wandering to very great dis- 

 tances in its native forests.* It may be called 

 the Vagabond Plant-louse {Pemphigus vagct- 

 bundus, Walsh), and is represented in Fig. 88. 



•See Proc. Enl. Soc, Phil., I, p .IM. where the fly is de- 

 scribed, andll, p. 462, where the s«ll is described. As to 

 the generic determin.ition of thia Plant-louse, see JbitI VI., 



