102 



THE AMERICAN ENTOMOLOGIST. 



be, namely upon the leaf instead of ujion the 

 twig, diflered in no respect from those that 

 occurred upon the adjoining twig- ! So definitely 

 are the form, size, color and texture of these sin- 

 gular i)roduction8 determined by the insect that 

 cause the abnormal growth on the infested plant, 

 so little does it matter from what parlicular part 

 of the plant the abnormal growth is developed! 

 Neither does it make any difteronce, as a general 

 rule, if the same species of gall-making insect 

 operates upon distinct species of plants belong- 

 ing to the same botanical genus. We have col- 

 lected, for example, numeroiis instances where 

 the same Gall-fly (C'//Hi^«) attacks distinct but 

 allied species of oak, and yet produces^ galls 

 that are entirely uudistinguishable, no matter 

 upon what species of oak they occur.* 



AVe are all of us so familiarized wilh one or 

 more of the wonderful processes by which ani- 

 mal and vegetable organisms i-eprodiice them- 

 selves, that it seems in no wise astonishing that 

 a sheep, for example, should generate a sheep, 

 a honey-bee a honey-bee, an oak an oak, and a 

 cabbage a cabbage. In all such cases, however, 

 an animal rcpi'oduces an animal, or a vegetable 

 reproduces a vegetable, and the same species, 

 whether animal or vegetable, reproduces an 

 almost exact image of itself either iu the next or 

 in some subsequent generation. But in the case 

 of galls, we have the \ery astonishing and 

 otherwise unparalleled fact of two organisms, 

 the one animal the other vegetable, cooperating 

 together to generate a third organism, entirely 

 different in all its characters from any thing that 

 either of the two parent organisms is capable 

 by itself of producing, and just as definite and 

 invariable in shape, size, texture and color, as 

 animal and vegetable productions that belong 

 to the same species usually are. Take, for in- 

 stance, a thousand "oak-apples"' (Fig. 78) 

 off black oak, and a tliousand apples from 

 an apple-tree. You will find that the former 

 resemble each other, both externally and inter- 

 nally, quite as closely as do the latter. Yet to 

 produce an apple all that is required is a living 

 and growing apple-tree of sufficient age; while 



•See Proc Ent. Soc. Phila. Ill, jk |-,39, u.jI.-, TIu' ruU 

 ri-sembling the oali-bullet gall (Q. globulu-i, Fitrh; «h;rV i» 

 there mcutioued aa occurring ouBuiToak, hiis Ixrn iiiicc 

 ascertained by us to be produced bv a di-linct ^p.i-ies of 

 Gall-fly from that which produces the oak-hulhi ^'all. The 

 sail it>rlr hu- Ihi- same very reniarliable iiitirnal ^Irurture, 



to produce au •• oak-apple " there is necessarily 

 required the joint co-operation of a gall-fly and 

 an oak, the first an animal, the second a veget- 

 able organism : and if either the gall-fly or the 

 oak were swept out of existence to-raorrow, the 

 oak-apple tliat they unite to produce would at 

 the very same time cease to exist in this world. 



The insects whicli are known to be the archi- 

 tects of galls are by no means an isolated group, 

 but belong to several different Families in no 

 less than five different Orders. They may be 

 enumerated as follows : The Snout-beetles and 

 the Long-honicd Beetles {Coleoptera) , the Saw- 

 flies and the Gall-flies (Ilymenoplera), the 

 Tinea and Tortiix Families {Lepidoptem) , the 

 Flea-lice {F^njUa). Plant-lice and Baik-lice (7/o- 

 mnptera), and the Gall-gnats and certain groups 

 belonging to the great Musca Family {Diptera). 

 In none of these Families is the gall-making 

 faculty universal, and in not many of them is it 

 general, but is on the contrary confined to par- 

 ticular species, the very same genus often con- 

 taining certain species that make galls and cer- 

 tain others that do not.* Besides the above 

 gall-making Families, all of which are true 

 Insects, many of the Mites {Acarus family), 

 which ai-e not true insects, construct upon vari- 

 ous trees galN ni' no very conspicuous size, 

 shape or striuiuic. (See Ameu. Extom., p. 57). 



Galls originate in two distinct modes, either 

 first, by the mother insect depositing one or 

 more eggs in or on the part of the plant which 

 she attacks, or second, by a young larva station- 

 ing itself upon a leaf or other part of a plant, 

 and iiTitating its surface with the organs of its 

 mouth, until a hollow is gradually formed which 

 eventually becomes a more or less tightly closed 

 sack, inside which the larva develops to matur- 

 ity and propagates its species. In this latter 

 case, which is peculiar to the Plant-lice, the 

 Bark-lice and the Mites, young larvse born 

 within the gall frequently stray away through 

 the partially open nuiuth of the enclosing sack, 

 and found new galls the same season either 

 upon the same or upon adjoining leaves. This is 

 the rule with gall-making Bark-lice and Mites. 

 But in galls made by Plant-lice, the entire brood 

 of larvae reared within the gall remain therein 

 till they have most of them reached maturity 

 and acquired wings. The gall then, by a beau- 

 tiful provision of nature, gapes open to allow of 

 their escape, usually at the month of the sack 

 formed by the mother insect, but in certain 

 cases in some other part of the sack. 



It will thus be seen that this second mode of 



•As, for example, the genus Xetnatm among the SBW-flieH 

 and the genus Cecidomi/w among the (iatl-gnuts 



