TEEMINOLOGY OP THE EXOSKELETON. 
11 
§ 1. TERMINOLOGY. 
(a) the exoskeleton. 
Aphides show in their larval condition many resem- 
blances to both the Coccidse and the Oicadidse. Like 
them, they possess soft yielding bodies, which are 
capable of considerable distension. When contracted 
by the partial loss oE their juices, the skins of these 
bodies are thrown into more or less marked folds or 
corrugations. 
The general aspect of Aphis may be described thus : 
— Body soft and yielding ; usually globose or oval, 
rarely linear. The bodies of the larvse are often heavy 
and inflated, and disproportioned to the size of the 
legs. The exterior integument of exoskeleton has but 
little rigidity, and does not show the dense coriaceous 
texture seen in most insects. Aphides, therefore, 
exhibit but little muscular activity, and except by 
stratagem are almost defenceless against their numer- 
ous enemies. 
The body is divided into rings or somites, but much 
discussion has arisen as to the normal number ; 
indeed, the number is inconstant. In some species 
certain rings are either hidden, or entirely suppressed. 
At the posterior end, mostly, but not always, two 
remarkable duQts occur, which generally project above 
the surface of the back. These are the well-known 
cornicles, nectaries, or siphuncles. 
A suctorial beak is folded on the breast, through 
which the insect pumps up the juices of the leaves, 
roots, or stems, of the various plants which form its 
nourishment. 
Although the family shows a great diversity in tints 
and markings, neither characteristics are of so constant 
