4 THE POPULAR SCIENCE MONTHLY. 



tennse, the third or terminal much the longest, and by carrying its 

 wings overlapping flat on the back instead of roof-fashion. It belongs 

 to the whole-winged bugs {Homopterd)^ and osculates between two 

 great families of that sub-order, the plant-lice [Aphididce) on the one 

 hand and the bark-lice {Coccidm) on the other. In the one-jointed tar- 

 sus of the larva or newly-hatched louse, and in being always oviparous, 

 it shows its affinities with the latter family ; but in the two-jointed 

 tarsus of the more mature individuals, and in all other characters, it is 

 essentially aphididan. " In every department of natural history a spe- 

 cies is occasionally found which forms the connecting link between 

 two genera, rendering it doubtful under which genus it should properly 

 be arranged. Under such circumstances the naturalist is obliged to 

 ascertain by careful examination the various predominating character- 

 istics, and finally place it under the genus to which it bears the closest 

 affinity in all its details." So wrote Audubon and Bachman twenty- 

 eight years ago ; ^ and what is true of genera is equally true of species, 

 families, and of still higher groups. In the deepest sense all iNTature is a 

 whole, and all her multitudinous forms of animal and vegetal life are so 

 closely interlinked, and graduate into each other so insensibly, that in 

 founding divisions on too trivial differences we subvert the objects of 

 classification. Thus, instead of founding a new family for this insect, 

 as Dr. Shimer did, and as there seems a tendency on the part of others 

 to do, it is both more consonant with previous custom, and more sensi- 

 ble in every way, to retain it among the Axjliididm. 



BIOLOGICAL. 



Different Forms which the Iis^sect assumes. — Xot the least in- 

 teresting features in the economy of our Phylloxera are the different 

 phases or forms under which it presents itself. Among these forms 

 are two constant types which have led many to suppose that we have 

 to do with two species. The one type, which I have, for convenience, 

 called gallmcola^ lives in galls on the leaves ; the other, which I have 

 called radicicola, on swellings of the roots. The subjoined table will 

 assist to a clear understanding of what follows. 



Type 1. OalloBcola. {VitifoUce, Fitch. Pig. 3,^1 ff, ^0 



Type 2. Padicicola. — 



a, Degraded or Wingless Form. (Fig. 4, e,f, g.) 



/3, Perfect or Winged Form. (Fig. 5, g, h ; Fig. 7, 5.) 



Type Gall^cola ok Gall-ixhabiting. — The gall or excrescence 

 produced by this insect is simply a fleshy swelling of the under side 

 of the leaf, more or less wrinkled and hairy, with a corresponding de- 

 pression of the upper side, the margin of the cup being fuzzy, and 

 drawn together so as to form a fimbriated mouth. It is usually cup- 

 shaped, but sometimes greatly elongated or purse-shaped (Fig. 2, a, b). 

 ' " Quadrupeds of North America," vol. i., p. 215. 



