APHIDES. 171 



"When the insect is perfect within, it moults again, and 

 appears with the full amount of limbs, and all the 

 powers to which it ever attains. 



A description of the method of change — that is, of 

 the whole operation of moulting from the commence- 

 ment up to the insect stepping out of its cast clothing 

 and standing perfect, besides its almost precise 

 counterpart — will be found at pp. 21, 22. 



It is useful to know exactly how this change occurs, 

 — to see it for ourselves, and to be able to show it to 

 others, — because, though the little wingless insect 

 vermin may be doing no great harm, as a few here 

 and a few there, yet they will grow bigger presently ; 

 they will by no means give us a season of peace in the 

 middle of their lives, and afterwards they will be able 

 to lay eggs, and will multiply. It is, therefore, well 

 to know and to be able to show that the little creature 

 we hardly see is the same that will by-and-bye (if it 

 is, say, an Aphis here, or a Locust in warmer countries) 

 cause broadcast loss and trouble. 



The order of the Homoptcra, or " similar-winged," 

 which includes, amongst the especially injurious kinds, 

 the great family of the Aphides or Plant-lice, takes 

 its name from the four wings being similar, that is, 

 membranous ; whereas in the very nearly allied order 

 of Heteroptcra, or dissimilar- winged, there is a thick 

 coriaceous or leather-like patch at the base of the fore 

 wings. They do not feed by biting, but by suction. 

 The upper and under pairs of jaws are lengthened into 

 long bristle-like growths, and enclosed in the length- 

 ened lower lip. The whole apparatus forms a kind of 

 beak, by means of which the insect pierces the soft 

 parts of the plants on which it feeds, and draws out 

 the juices. Thus it not only hurts the plant by suck- 

 ing away the sap, but also does great harm by the 

 number of little holes which it pierces in whatever 

 part it attacks. 



The insects of this order differ widely in form ; from 

 that of the Scale Insect, fixed like an oyster- or mus- 



