3o6 Phylloxera. [zoe 



ians and'Coccides; they are wafted on the breeze in a style but 

 little superior to that of the Medusa palpitating in the currents of 

 the ocean. Why should then the Phylloxera not share the fate of 

 analogous organisms? 



I do not refer here to the crowd of minute insects found in aban- 

 doned spider webs, because the minuteness of the Phylloxera would 

 prevent to a considerable degree its detection in the dust and 

 variety of debris collected at such a locality, but the smooth, clear 

 surface of the water cannot conceal any object minute as it may be, 

 provided it be not transparent. 



I do not deny the possibility of these minute things being carried 

 in the plumage of birds, the clothing of vintners, or by the evening 

 breeze from spot to spot, from vineyard to vineyard. On the con- 

 trary, I am certain that all the isolated centers from which irradiates 

 destruction are originated by winged individuals carried thither. 



The only point in which experiments have taught me to differ, 

 is the idea of a regular development "of the winged generation ac- 

 cording to a law analogous to the one that rules the development 

 of the winged generation in the rest of the known Aphidians and 

 Coccides. In these insects the development to the winged and to the 

 sexual generations runs through a well defined cycle, corresponding 

 more or less, but always in some way with the cycle of the seasons 

 of the year. 



Now my own experience has convinced me that the development 

 of the winged generation is entirely independent of the seasons, or 

 any regular cycle. The law that rules its dimorphism is analogous 

 to the law that rules the dimorphism of the Lepidopterous genera 

 CEcedcus, Solenobia, Tateporia, and perhaps other sack-bearers. 

 Here a parthenogenesis of wingless individuals is going on ad in- 

 finiium, and the collector who expects specimens of the winged 

 male is constantly disappointed till suddenly winged males are 

 produced, which, mating with the wingless females, reproduce an- 

 other series of parthenogenetic generations. 



The circumstance that in Phylloxera the winged generation serves 

 only as an introduction to the sexual generation, and is not the 

 sexual itself, forms a difference immaterial to the present discussion, 

 although it is highly interesting as an instance of the power of 

 adaptation in itself. 



In reeard to CEceticus. the evpfM^flnnnl <-;r/-i.mGfon/-^Q whirh cause 



