26 



heard of for years: — Although in 1866 these leaf-galls covered th«^ 

 leaves of the wild Frost Grape and of the cultivated Clinton near 

 Eock Island, Illinois, and, so far as I could hear, throughout the State, 

 yet in 1867 on the most diligent search not a single one was to be 

 found, even on vines which had swarmed with them in the preceding 

 year. 



Previous to what I published on the subject, authors had alway;? 

 supposed that this Gall-louse attacked indiscriminately all kinds £)i 

 grape-vines. I was led to remark that it was not so, because I had 

 discovered it to be a general, though by no means a universal rule, 

 both with Plant-lice {Aphis family) and with Bark-lice {Coccus 

 family,) that the same species of insect is confined to the same species 

 of plant. Even when a species, belonging to one of these two fam- 

 ilies of insects, inhabits promiscuously two or more species of plants, 

 these plants will usually be found to belong to the same botanical 

 Genus, and invariably to the same botanical Family. We shall meet 

 with another illustration of the practical importance of attending to 

 this law of nature, when we discuss the history and habits of the 

 Apple-root Plant-louse in chapter 10, 



them was found, the other one would be found there also., and, in all proba- 

 bility, always in the same relative proportion. 



If any one doubts the validity of the above statement, he has but to 

 refer to the figure of the wings of the so-called male Dact. vitifolio', in Dr. 

 Shimer's Paper (fig. D, page 1) ; and he will see at once that it displays the 

 unmistakable wing-neuration of the genus of Plant-lice which Dr. Fitch con- 

 sidered as probably identical with the European genus Phylloxera, (see my 

 fig. of it, Froc. Ent. /S'oc, Phil., I., p. 297, fig. 8) — which I have since pro- 

 posed to name Xcrophylla {ibid. VI., pp. 282 — 3, note) and to which the 

 Plant-louse of my Carycc globuli gall belongs. This figure of Dr. Shimer's, 

 it may be added, is totally unlike a drawing of the wings of the veritable male 

 Dact. lutifoliii'. which was kindly executed for me by Mr. Cresson, from speci- 

 mens presented to the Entomological Society of Philadelphia by Dr. Shinier 

 himself, and which drawing I sometime ago comnuniicated to Baron Osten- 

 Sacken. For, in this last, the neiiration of the front wing is almost exactly 

 identical with that of a male Bark-louse (see Westw. Introd., II., p. 443, 

 fig. 7 ) , and the hind wing lacks ^entirely on its front margin the character- 

 istic hook to fasten on to the hind edge of the front Aving, which is found 

 in all the genera of Plant-lice with which I am acquainted. Dr. Shimer, in- 

 deed, lays great stress upon the absolute necessity of such drawings being 

 executed from the living or recent insect. (Page 5, note.) So far as re- 

 gards the body of the insect, this is true enough ; but every entomologist 

 knows, that the ivinys of any insect can be drawn just as accurately from the 

 dried as from the recent specimen. 



With similarly imfortunate results, this same author has recently re- 

 described and re-named, as Hamamelistes cornii, a gall-making Plant-louse 

 (Honnaphis haniamclidis. Fitch), which had been alreadv named and de- 



