HEMIPTERA. 1 1 3 



tect it from the attacks of carnivorous insects and spiders. On the 

 other hand, its skin is without doubt so constituted that it would 

 perspire too freely if it were exposed to the air, and the insect would 

 very soon die dried up. Whatever explanation may be given of the 

 necessity for this semi-aerial, semi-liquid medium, it is easy to verify 

 the fact that the larva of the Aphrophora cannot live long out of its 

 frothy envelope. If withdrawn from it, the volume of its body 

 diminishes perceptibly, and the poor animal dies, like a fish taken 

 out of its natural element. 



The insects which live in this froth are six-legged grubs (Fig. 84), 

 which, when the froth is cleared from them, walk 

 quickly enough on the stalks and leaves of plants. 

 They are green, with the belly yellow. 



De Geer wished to know how they produced 

 this singular froth, and found out in the following 

 manner : He took one of them out of its frothy 

 dwelling, wiped it dry with a camel's-hair pencil, and 

 placed it on a young stalk, recently cut from the 

 honeysuckle, which he put into water in a glass, in 

 order to preserve its freshness, and this is what he 

 observed :-- 



" It begins," says the Swedish naturalist, "by fixing 

 itself on a certain part of the stalk, in which it inserts 

 the end of its trunk, and remains thus for a long 

 time in the same attitude, occupied in sucking and filling itself 

 with the sap. Having then withdrawn its trunk, it remains there, 

 or else places itself on a leaf, where, after different reiterated move- 

 ments of its abdomen, which it raises or lowers and turns on all 

 sides, one may see coming out of the hinder part of its body a 

 little ball of liquid, which it causes to slip along, bending it under 

 its body. Beginning the same movements again, it is not long in 

 producing a second globule of liquid, filled with air like the first, 

 which it places side by side with, and close to, the preceding one, 

 and continues the same operation as long as there remains any sap 

 in its body. It is very soon covered with a number of small globules, 

 which, coming out of its body one after the other, tend towards the 

 front part, aided in this by the movement of the abdomen. It is all 

 these globules collected together which form a white and extremely- 

 fine froth whose viscosity keeps the air shut up in the globules, and 

 prevents its froth from easily evaporating. If the sap which the 

 larva has drawn from the plant is exhausted before it feels itself suf- 

 ficiently covered with froth, it begins to suck afresh, until it has got 



