OF THE STATE ENTOMOLOGIST. 



spring, these young lice work off their winter coat, and, growing apace, 

 commence to deposit eggs. All, without exception, so far as I have 

 seen,* become mothers, and assume the degraded form (a) already 

 described. 



At this season of the year, with the exuberant juices of the plan ti 

 the swellings on the roots are large and succulent, and the lice plump 

 to repletion. One generation of the mother form (a) follows another — 

 fertility increasing with the increasing heat and luxuriance of sum- 

 mer — until at least the third or fourth has been reached before the 

 winged form (/5) makes its appearance in the latter part of June or 

 early in July. (11) 



Such are the main features which the development of the insect 

 presents to one who has studied it in the field as well as in the closet. 



This polymorphism, which at first strikes us as singular, is quite 

 common among plant-lice, and many curious instances of still more 

 striking character might be given. Even the differences themselves 

 between gallmGola and radicicola are more apparent than real. Indi- 

 viduals of the latter are often met with, which, in the comparative 

 obsoleteness of their tubercles, are almost undistinguishable from the 

 former; and the tubercles, like many other purely dermal appurte- 

 nances, are of an evanescent and unimportant character. Many insect 

 larvae, which are normally granulated with papillae, not unfrequently 

 have these more or less obsolete, and at some stages of growth have 

 the skin absolutely smooth. The same thing holds true of tubercles, 

 which, as in the case of the Imported Currant-worm {NemaUis 'ceniri- 

 casus Klug), to be presently treated of, are often completely cast off 

 at a molt. In Phylloxera they are very variable in size, as we shall 

 see, in Eileyi; and in querciis^ according to several reliable authors, 

 the tubercles which are characteristic of the species in Southern France 

 are entirely wanting around Paris. If we carefully study ihemmvas- 

 iaifix, we shall find that they consist of points where the granulated 

 skin is gathered around a fleshy hair in little rugosities, and becomes 

 darker (Fig. 5, i). They do not occur in the newly hatched larva, are 

 not visible immediately after each molt, and are lost again in the 

 winged individuals. In the form gallm-ola we shall find, upon careful 

 examination, especially of the exuvia, that, as Max.Cornu has shown, 

 there are rows of short hairs, extending beyond the natural granu- 

 lations, and corresponding to those on the tubercles of radicicola. 

 ■*These hairs are more visible on the younger and smoother lice after the 

 first molt; and they are sometimes so stout,'particularly on the abdo- 

 men, as to remind one of those on Rileyi^ to be described. The ven- 

 tral characteristics of the two types are identical. 



• I ha\e examined tliousaiids ill the vineyard in eurly rtpring-, siiul other thousands reared^ artlQ- 

 ■oiidly in a warm lotim in winter. 



