86 SIXTH ANNUAL REPORT 



it to a new climate. Therefore, putting aside the above explanations, what remains to 

 account for the fixtality of our [the European] vines in the United Statet^? A single 

 thing, very small in appearance, very powerful in reality ; hidden, and hence, for a 

 long time ignored, but very manifest when once we have learned to see it, and follow, 

 by careful study, its effects, tirst on the roots, then on the entire vine. This insigniti- 

 cant atom, which is legion, is none other than the Phylloxera. With this simple and 

 palpable cause, first recognized by Eiley, and which my recent studies in America have 

 rendered to me most evident, all the facts may be connected and explained." 



(25) Phylloxera Rilkyi Lichtenstein.— This insect, which, from specimens sent 

 to him, Lichtenstein has kindly named after me, but of which I have not yet seen his 

 desciiption, may be characterized in comijarison with vastairi.c. 



Apterous $— Length O.OlGinch, or rather more than a third as large as vastat?-ix; 

 with which it agrees in color. Proportionally more slender, with the abdomen more 

 tapering. Body insected and covered with tubercles very much as in wingless radiei- 

 cola form of vastatrix, but with an additional pair on the head, and those on the seventh 

 abdominal joint always distinct. These tubercles concoiorous with the bodj', fleshy, 

 more or less elongate^from 1-12-1-6 the width of middle body — and surmounted at 

 tip with a short, dark hair. The anterior turbercles longest; the lateral outline show- 

 ing a series of thirty-six such tubercles, nearly equidistant, springing at about right 

 .angles from surface. The intermediate dark points, on thoracic insections, also as in 

 vastatrix. Antenna- precisely as in vastatrix. Legs with the ends of tibiaj more- 

 swollen, and the claws more prominent. Venter, with a dusky tubercle just inside 

 each coxa. Pupa, (Fig. 18, a) with the tubercles prominent, and the pale mesothoracic 

 portion occupying more of the body. Winged insect, (Fig. IS, b) with the dark meso- 

 thoi'acic band much as in vastatrix:, the wings more slender and somewhat more 

 fuliginous, with the costal angle more produced and blunt, and the hook larger on 

 secondaries; the antenn;c (Fig. 18, e) with the third joint and the horny parts propor- 

 tionally longer. Also presenting two forms of body and wing as in vastatrix, the un- 

 doubted $'s also much the more numerous. Newly-hatched larva smooth, with dark 

 limbs and eyes, the tubercles increasing with each molt, and sometimes noticeable 

 before the first. 



The species is less prolific, and the eggs proportionally laiger, than in vastatrix., 

 but in the tarsal characters of the young and more mature individuals, and in all other 

 features not mentioned, there is perfect correspondence. The tubei'cles, as already in- 

 dicated, are very variable in size. Numerous specimens examined. 



(2G) I have such faith in the unity of habit and unity of biological traits in the 

 same genus, that I fully expect that future inquiry will show that the European Oak 

 Phylloxera has a similar whiter habit, and that the apterous and mouthless sexual in- 

 dividuals discovered by Balbiani, in the European species, exist in ours ; and the same 

 argument will apply to the Grape Phylloxera. What is clear, however, for the two 

 species here treated of, is, that the solitary and fecundated e^cr^ if jt occurs, is not neces- 

 sarily hibernal. The production of these sexed individuals may form a definite phase 

 in the annual development of either species; but as the number of viviparous parthe- 

 nogenetic generations, and the production of eggs in the true Aphides, are known to 

 depend more on temperature and external conditions than on any definite biological 

 inherency, 1 strongly suspect that the same will hold true of Phylloxera; and that the 

 sexed individuals, while produced mostly in the fall, may also be produced at other 

 seasons ; further, that the young from the impregnated e^g!^ will differ in nowise from 

 tliose from the unimpregnated, except in their greater vigor and fertility. 



