PHYLLOXEEA. 43 



in the later generations. In the larvaa the head is 

 united to the body without any apparent constriction 

 to form a proper thorax. Cornicles none. 



M. Lichtenstein uses the tubercles of the antennas as 

 specific characters in the genus. 



This genus is, in a qualified sense, exclusively 

 oviparous, for the true ovum applies only in strictness 

 to the produce of the perfect sexes. Prof. Passerini has 

 included all the known forms of Phylloxera under the 

 tribe Chermesinas; but more recently M. Lichten- 

 stein, who perhaps has studied this small group of 

 insects as completely as any one, sees sufficient differ- 

 ences in their habits and general characters to separate 

 them not only from the ChermesinaB, but from the 

 Aphidinaa altogether. Prof. Targioni Tozzeti also 

 contemplates a similar dissociation, and has proposed 

 that the group should be capitalised under the name 

 Phylloxerites.* 



I feel indisposed to assert how far Phylloxera has 

 or has not a natural classification under the family of 

 Aphides. Hard and fast lines of^demarcation are almost 

 impossible to be defined for nearly allied forms, and 

 much Avill depend on the relative values and importance 

 given by systematists to any particular deviation from 

 the type. For the present, therefore, I prefer to 

 leave Phylloxera (which contains perhaps only a single 

 known genus) to the family assigned to it by Passerini 

 and other writers. Without such a grouping, indeed, 

 the insects now to be described could have no place in 

 this Monograph. 



General remarks on the genus Phylloxera. 



It may be well said that of all pestiferous Aphidian 

 genera Phylloxera is the most destructive. Fortu- 

 nately in this country we have felt no great injury 

 from the only known indigenous species. From the 



* 'Bull, de la Soc. Ent, Ital.,' 1875, f. 281. 



