HEMIPTERA. 121 
they leave their mother. The young ones set off and mount or 
descend till they reach one end of the crowd, and there each 
takes up its position, like a cardboard capucin (capucin de carte), 
in such a manner that the head is just behind the plant-louse 
which precedes it. There they bury their trunks in the vegetable 
tissue, and set to work to imbibe the sap. 
Small as is the trunk of the plant-louse, yet when there are 
thousands of those little beings fixed to the stalk or the leaves of 
a plant, it is evident that it must suffer. And so the plant- 
louse is, in truth, one of the most terrible enemies of our agricul- 
tural and horticultural productions, and the exact list of the 
ravages which it occasions would be indeed interminable. We 
will confine ourselves to a few examples. For some years 
the lime-tree aphis has seriously attacked the lime-trees of the 
public promenades of Paris. The peach-tree plant-louse 
causes the blight of the leaves of that tree. It is to these 
prolific little parasites that are due, in a great number of cases, 
the contortions of leaves and of the young shoots of trees of all 
sorts. 
These insatiable depredators cause sometimes a still more re- 
markable alteration. On the leaves of elms one sees often bladders, 
round and rosy, like pommes d’api. On opening these bladders 
one finds that, they are inhabited by a species of aphis. On the 
black poplar grow galls of different kinds, some from the leaf 
stalks, and others from the young stems. They are rounded, 
oblong, horned, and twisted in a spiral. Other galls show them- 
selves on the leaf itself. They are all inhabited by plant-lice, 
differing from those of which we have given a description above, 
in the extremity of their abdomen not presenting the two 
remarkable horns to which we shall have later to call the 
attention of the reader. The body is generally covered with a 
long and thick down. 
Of this genus, the species, alas! so unfortunately celebrated is 
the Apple-tree Aphis (Myzoryle mali), which attacks that tree. 
This insect is of a dark russet brown, with the upper part of the 
abdomen covered with very long white down. Its presence was 
announced for the first time in England in 1789, and in France, 
in the department of the Cotes-du-Nord, in 1812. In 1818,it was 
