78 AMEEICAISr GRAPE GKOWING 



pupa state, they rise in the air and spread to new vine- 

 yards, where they deliver themselves of their issue in the 

 form of eggs or egg-like bodies — usually two or three in 

 number, and not exceeding eight — and then perish. 

 These eggs are of two sizes, the larger about 0.03 inch 

 long, and the smaller abouti three-fifths of that length. 

 In the course of a fortnight they produce the sexual indi- 

 vidual, the larger ones giving birth to females, the smaller, 

 to males. These sexual individuals are born for no other 

 purpose than the reproduction of their kind, and are 

 without means of flight, or of taking food, or excreting. 

 They are quite active and couple readily ; one male be- 

 ing capable, no doubt, of serving several females, as Bal- 

 biani found to be the case with the European quercus. 

 The abdomen of the female, after impregnation, en- 

 larges somewhat, and she is soon delivered of a solitary 

 egg, which differs from the ordinary eggs of the parthe- 

 nogenetic mother only in becoming somewhat darker. 

 This impregnated egg gives birth to a young louse, which 

 becomes a virginal, egg-bearing,_ wingless ' mother, and 

 thus recommences the cycle of the species' evolution. 

 But one of the most important discoveries of Balbiani is 

 that, during the latter part of the season, many of the 

 wingless,. hypogean mothers perform the very same func- 

 tion as the winged one ; i. e., they lay a few eggs which 

 are of two sizes, and which produce males and females, 

 organized and constructed precisely as those born of the 

 winged females, and, like them, producing the solitary 

 impregnated egg. Thus, the interesting fact is estab- 

 lished that even the winged form is by no means essen- 

 tial to the perpetuation of the species ; but that, if all 

 such winged individuals were destroyed as fast as they 

 issue from the ground, the species could still go on mul- 

 tiplying in' a vineyard from year to year. We have, 

 therefore, the spectacle of an underground insect posses- 

 sing the power of continued existence, even when confined 



