414 THE PHYTOPHTHIRIA. 



A large number of exotic species have the pro- 

 thorax greatly enlarged and sometimes produced back- 

 wards, so as to cover the whole upper part of the 

 body and wings, whilst in other cases it forms spines 

 and processes of the most grotesque shapes, giving 

 the insects a most singular aspect. Of this group we 

 have only two British species, the commonest of which 

 (Centrotus cornutus) is found principally in and about 

 woods upon trees and various plants, whilst the other 

 (Centrotus Genistas) generally occurs upon the com- 

 mon Dyer's weed (Genista tinctoria). In the Cen- 

 trotus cornutus, which measures about a third of an 

 inch in length, the prothorax is armed with a pair of 

 strong acute horns, and its posterior portion is pro- 

 duced into a long angular spine, which reaches nearly 

 to the posterior extremity; whilst the C. Genista, which 

 is considerably smaller, has the prothorax very convex 

 and produced into an acute spine behind, but desti- 

 tute of any horns upon its sides. 



Plants of every kind in our gardens, fields, and 

 woods are constantly infested by an immense number 

 of minute soft insects, well known to most people 

 under the names of Plant-lice or Aphides. They are 

 sometimes wingless, and sometimes provided with 

 four wings, of ^which* the anterior are much larger 

 than the p6st$Ror, the head bears a pair of rather 

 long antennae, the rostrum appears to spring from the 

 breast between the fore-legs, and the tarsi are com- 

 posed only of two joints. They form the tribe of the 

 PHYTOPHTHIRIA*, and although of small size, they are 

 amongst the most interesting of insects, not merely 

 * Gr. phuton, a plant ; phtheir, a louse. 



