196 



INSECTS. 



feed on the sap, their puncture being often followed by the formation of gall-like 



swellings. The figured Psylla genistce feeds on the broom, but other species are 



found on apple and pear trees. The plant- 

 lice (Aphidce) are small insects, which make 

 up in numbers what they lack in size, and, 

 owing to the injury they inflict on plants, 

 must be ranked amongst the greatest pests 

 with which the gardener and horticulturist 

 have to contend. They are those soft, pulpy 

 little creatures, with rather long antennae 

 and conspicuous round eyes, so commonly 

 seen crowded together on the under side of 

 leaves, in buds and flowers, in clefts in the 

 bark of trees, and sometimes even on the 

 roots. The antennse are composed of from 

 three to seven joints, on some of which are 

 a number of curious rounded pits, probably 

 of a sensory nature. The eyes are placed 

 on the sides of the head, and each has 

 often a sort of supplementary eye attached 

 to its hind border ; while in the winged 

 aphides there are three ocelli on the crown 

 of the head. The beak is composed of 

 three joints ; and the tarsi are two-jointed 

 and terminate in two claws. Wings, as a 

 rule, are found only in the adult males and 

 in some of those generations of asexual 

 individuals to be mentioned presently. The 



fore- wings are longer than the hind-pair, and placed in repose like a roof over the 



hind part of the body. Both pairs 



have a scanty venation, consisting in 



each wing of a single longitudinal 



vein, and of some simple or forked 



branches given off obliquely from it. 



The number of species is considerable, 



and there is scarcely a single kind of 



plant that does not suffer as the 



special host of some one or more. 



Many are green, whence the name of 



green -fly by which they are com- 

 monly known ; others are black, red, 



or some other colour. 



1. Ledra aurita ; 2, The same seen from the side 

 (both enlarged) ; 3, Aphrophora spumaria ; 4, 

 Larva of the same. 



Centrotus cornutus (slightly enlarged). 



Psylla genistce (six times nat. size). 



They are usually named after 

 the plants on which they more particularly live, 

 though each species is not necessarily confined to one 

 kind of plant. Thus we have the plant-louse of the 

 rose (Aphis rosce) ; the green aphis of the apple (A. 



