APHIS. 31 



Genus X.—APHIS,* Linn. 

 Blattlaus, Puceeon, Pidocchio, Plant-louse. 



Eostrum moderately long ; the last joint skittle- 

 shaped, and as long as the preceding. 



Antennse shorter than the body. Frontal tubercles 

 none or rudimentary. Seventh joint setaceous, and as 

 long as the third. 



Cornicles cylindrical, and equally thick throughout. 



Cauda short, sometimes hardly visible. 



Legs moderately long. 



Wings generally shorter than in the preceding 

 genera, but veining similar. 



During the lapse of the last twenty years several 

 perfect sexual forms of this genus have been discovered. 

 The males are sometimes apterous and sometimes 

 winged, and occasionally even both varieties occur in 

 the same species. As to the general character of 

 Aphis, it may be observed that all the forms show the 

 wings, antennge, and cornicles in a less developed state 

 than in SipJiono^^thora. 



An artificial grouping of this genus has been 

 attempted in the foregoing synopsis, and a certain value 

 has been given to the attribute of colour, just as has 

 been done in the synopsis appended to Sipliono'pliOTa. 



Passerini has adopted a similar course, but he has 

 made his first great division to depend on the varying 

 length of the tail. Prom the power possessed by 

 some Aphides of withdrawing this organ into the abdo- 

 minal cavity, I have not so prominently brought for- 

 ward this character. In some cases it is difficult even 

 to decide whether the insect possesses a true tail at all. 



Under the name Aphis was formerly comprehended 

 not only all the Aphidince, but also the allied tribes 



* For the derivation of the word Aphis vide Introduction to vol. i, 

 p. 4. 



