THE AMERICAN ENTOMOLOGIST. 



103 



the formation of galls is the exception, and tliat 

 the first mode, nunioly that when the mother 

 insect deposits one or more eggs on or in the 

 infested plant, is (ho rule. In the latter ease, 

 when bnt a single egg is deposited in one place, 

 the larva that develops from tliat egg forms bnt 

 a single cell, inside whicli it resides, as in. Fig. 

 78 a. The gall is (hen teelinieally said to be 

 •• monothalamous." i. c. one-celled. lUit when- 

 ever several eggs are deposited in one place, the 

 larvie developing therefrom inhabit several cells 

 enclosed in a common envelope, as in Fig. 8.'i, b. 

 The gall is then said to be '• polythalamons," 

 i. e. many-celled. In the second group of galls, 

 namely those made by Plant-lice. Mites, etc., 

 the inhabitants of tiic gall, however numerous 

 lliey may be, always resiile in'omisc-nously in 

 the same large cell or hollow. 



The number of galls formed by distinct spe- 

 cies of insects or mites upon various plants in 

 -Vmerica is very great, and a large proportion 

 of them are as yet undescribed and unknown to 

 science. Of those (hat occur upon trees and 

 shrubs, exclusively of herbaceous plants, we are 

 ourselves acquainted with nearly two hundred 

 different species, about a third part of which are 

 undescribed. In the following paragraphs, we 

 propose to give a brief account, illustrated by 

 tigures, of some of the more conspicuous ones 

 out of the whole number, made by three dif- 

 ferent Families of insects, namely the Gall-dies, 

 the Gall-gnats, and (he Plant-lice. 



(ialls made Ity Gall-flies. ((>«/>«.) 

 TuE Tkue ''Oak Aitle," as it is popularly 

 termed, (Quercus sjjoi)(/(/ira. Osten Sacken, 

 Fig. 78) occurs exclusively upon (he Black oak 

 (Quercus (inctoria). It commences its growth 

 in May, or as soon as the \oung leaves put forth, 



[fit;. 78.] 



(-'olor.s— ln-ab inHiile: Jello\vi^^h-b^o\vn outHii.le. 



and reaches its full size in a few weeks. The 

 central cell (Fig. 78 o) in which the larva rdRj 



sides becomes eventually hard and woody, but 

 the space between that cell and the external 

 skin or rind of (he gall is always complelely 

 tilled by soft, drab, spongy matter. By the fore- 

 part or middle of June both male and female 

 gall-flies (CV/'i''7J« </• sponr/ifica O. S.) eat tlieir 

 way out of a certain number — say about a fourth 

 part — of these galls, having developed into the 

 winged state from the larva in the centra! cell. 

 The hole by which the tly makes its exit is 

 shown at Fig. 78 b. Tiie remaining larvj* lie 

 dormant for more than two months, when they 

 cliange into tiie pupa state, and subsequently 

 about October e.at their way out in the form of 

 Gall-llies {Ci/nips q. acicidata, O. S.) closely 

 allied to and yet quite distinct from those pro- 

 duced iu June. Out of thousands of tliese 

 autumnal flies examined by us, all were females 

 with not a single male among them; and we 

 have experimentally ascertained, by colonizing 

 a number of these females upon isolated black 

 oaks known to be not previously infested with 

 oak-.ipples, that they cause oak-apples (o bo gen- 

 erated in the following spring upon such isolated 

 Black Oaks. From Oak-apples produced in (his 

 manner we have bred two .specimens of tlie 

 spring form of Gall-fly (g. sponcjiflca) which 

 exists in both sexes, and five specimens of the 

 autumnal form {q. acicidata) which exists ex- 

 clusively in the female sex. Finally, treating 

 these five autumnal specimens in the same man- 

 ner, i. e. placing them upon another isolated 

 Black Oak, we obtained galls in (he following 

 spring which produced (wo specimens of (he 

 spring form (^spongijica), (bus showing that the 

 autumnal form sooner or later reverts to the 

 spring form. Hence, as well .as from other con- 

 siderations, we may infer that the former is not 

 a distinct species but a mere "dimorphous" 

 female form of the Latter ; for otherwise, one 

 form could not generate the other form. As to 

 the supposed impossibility of females generating 

 without any sexual iutercourse with males, 

 there are many species of insects where no males 

 at all are known to exist.* 



• That evtu with those .species of iusectb where male.- iirr 

 entirely unknown males may occasionally make their ap- 

 pearance, thojigh perhaps only arter the expiation om 

 vears, we may infer, because there is a regular fc'iacl.itini 

 iVom one e.xtremity of the scale to another, 1st. In nio.t 

 Insects the sexes are about e.iual in .n"m'»'i;- -;|: ' ,\."T ,^ 

 groups, as for example m many f !/mj« " ^/^'•'');;^„ ''!,;, "^^ 

 5 tinies as numerous as the luales. .!'l. In the C.\nipirtou8 

 genus RAod«cs the males are generally ol extreme nim\_ 

 (th. In the lepidopterous Psyche hcltx, as we die assi ii 

 bv l)r Hagen, out of thousaiuls of specimens bieil wMbin 



■le la.t teji years by Prof. Siebokl. all were teniales: 1, it 

 lHi7 the male was ((iscovcred to occur, but m \ei.i small 

 nur.be sbv Prof. Clauss. .--.th. I>r. Haitig oug ago bred 

 ?i- he'gali thousands of fe.nales oi Cymp^ ./om, ^n.l nine 

 or ten thousand females of Cymps divim, -«,'t.hout a smS c 

 male among them; and we haye °"'-:;^„V/« ^^"\.^' .'i";. » V 

 tlinnsand females of Cymps q. punctata, Ba.ssett (— c. i;, 

 p'r/r" Wahlh from th?. B^'V^'if^o^t being able to discoye 

 on tlie closest examination a single male m the numbei . 



