Page:Popular Science Monthly Volume 5.djvu/22

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12
THE POPULAR SCIENCE MONTHLY.

highly improbable circumstance); for the characteristics which distinguish it are to be noticed in the pupa (Fig. 7, a), which is almost as broad as long, with very large wing-pads and strong limbs; while the winged insect does not, as we have seen, carry any eggs. But, whatever the true nature and functions of these problematic and gynandrous individuals, it would seem, from some exceedingly interesting observations lately made by Balbiani,[1] that they cannot be males, if there be any such thing as unity of habit and character among the species of the genus. Balbiani has made the curious discovery, in the annual development of Phylloxera quercus that the winged individuals, which appear in August, fly off to new leaves and deposit their

Fig. 7.
PSM V05 D022 Type radicicola.jpg
Type Radicicola.a, b, pupa and image of a gynandrous individual, or supposed male; c, d, its antenna and leg; e, vesicles found in abdomen.

unimpregnated eggs, to the number of five to eight. These eggs are of two different sizes, the smaller being readily separated from the larger. They hatch in about a dozen days, the smaller giving birth to males, and the larger to females, which have neither mouth-parts nor digestive organs, and neither grow nor moult after birth. The sole aim of their existence is the reproduction of the species, and they crawl actively about and gather in little multitudes in the crevices and interstices which are afforded them. The male, except in size, seems to differ from the female only in having a small conical tubercle, which serves as sexual organ. Coitus lasts but a few minutes, and the same male may serve several females. Four or five days after birth the female lays a solitary egg, which, increasing somewhat after impregnation, had caused her abdomen to swell and enlarge a little prior to

  1. "Comptes Rendus de l'Académie des Sciences de Paris," 1873, p. 884.