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THE POPULAR SCIENCE MONTHLY, 



highly improbable circumstance) ; for the characteristics which dis- 

 tinguish it are to be noticed in the pupa (Fig. V, 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 gv- 

 nandrous individuals, it would seem, from some exceedingly interesting 

 observations lately made by Balbiani,^ 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 individu- 

 als, which appear in August, fly oif to new leaves and deposit their 



Fio. 7, 



Ttpe Radicicola.- a, 5, pupa and imacro of a gynandroiip individual, or supposed male ; c, (?, 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 in- 

 terstices 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 fe- 

 male lays a solitary Qgg^ which, increasing somewhat after impregna- 

 tion, had caused her abdomen to swell and enlarge a little prior to 



' "Comptes Rendus de I'Academie des Sciences do Paris," 1873, p. 884. 



