Page:Popular Science Monthly Volume 5.djvu/21

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11
THE GRAPE PHYLLOXERA.

their way to the light of day, crawl over the ground and over the vines, and finally shed their last skin and assume the winged state. In this last moult the tubercled skin splits on the back, and is soon worked off, the body in the winged insect having neither tubercles nor granulations. These winged insects are most abundant in August and September, but may be found as early as the first of July, and until the vines cease growing in the fall. The majority of them are females, with the abdomen large, and more or less elongate. The veins of the front wing are not connected (Fig. 6, a), and, by virtue of the large abdomen, the body appears somewhat constricted behind the thorax. From two to five eggs may invariably be found in the abdomen of these, and are easily seen when the insect is held between the light, or mounted in balsam or glycerine. A certain proportion have an entirely different shaped and smaller body, the abdomen being short, contracted, and terminating in a fleshy and dusky penis-like protuberance, the limbs stouter, and the wings proportionally larger and stouter, with

Fig. 6.
PSM V05 D021 Pterogostic characters.jpg
Pterogostic Characters.a, b, different venation of front-wing; c, hind-wing; d, e, f, showing development of wings.

their veins connecting (Fig. 6, b). This shorter form (Fig. 7, b) never has eggs in the abdomen, but, instead, a number of vesicles (Fig. 7, e), containing granulations in sacs. These granulations have much the appearance of spermatozoa, and seem to have a Brownian movement, but are without tails.

This form has been looked upon as the male by myself, Planchon, Lichtenstein, and others. Yet I have never succeeded in witnessing it perform the functions of the male, nor has any one else that I am aware of. The males in all plant-lice are quite rare, and, in the great majority of species, unknown. Where known, this sex bears about the same relation to the female as the shorter and smaller Phylloxera just described does to the larger. These same differences observed in the winged insects obtain in the other species of the genus that are known, and have always been looked upon as sexual. Signoret, an authority on these insects, once so looked upon them,[1] but has lately declared the shorter form to be a female emptied of her eggs. If this be so, then the eggs must be laid before the insect arrives at maturity (a

  1. "Annales de la Société Entomologique de France," 1867, pp. 301, 308.