264 THE ENTOMOLOGIST. 
rambling would be useless, since the upper cuticle and the 
parenchyma of the leaf, which constitute their principal food, 
are always within reach without the trouble of moving. 
These they consume in a very methodical manner, leaving 
the lower cuticle entire; this very soon dies, withers, and 
turns brown, making the whole tree look as though covered 
with dead leaves. 
The process of exuviation, or casting of the skin, obtains 
in this, as in all other larva. Before it is performed the little 
slug wanders about the leaf with more freedom of movement 
than usual; it is no longer glued, as it were, to the cuticle. 
After the skin is cast the slug may be seen licking its old 
coat, an occupation which seems par ticularly enjoyable. The 
mandibles are also incessantly and actively at work; yet the 
cast clothing does not entirely disappear, although it is 
certainly diminished: the anterior part seems to be eaten, 
the hinder part neglected. This observation is made in con- 
sequence of the well-known propensity of certain lepidopterous 
larve to make a meal not only of the egg-shell from which 
they have just emerged, but also of the garments, which are 
from time to time thrown aside in favour of a new suit. What 
a saving might be effected if we humans could thus utilise our 
old clothes instead of feeding on beef and mutton, the price 
of which seems gradually advancing towards a point which 
will render the use of such viands impossible. The changing 
of the skin takes place in America five times. I cannot say 
that five is the number of ecdyses in England, as I have 
not counted the new suits worn by English slug-worms. At 
the last change the slug loses its jelly-like surface, and 
appears in a neat yellow skin without any viscidity. This 
occurs nearly a month after their first escape from the 
egg-shell; the head and segmental divisions are now quite 
as perceptible as in any other species of sawfly. Hence- 
forward it eats no more, but crawls down the trunk of the tree 
and buries itself in the earth: at the depth of three or four 
inches, each forms a neat little oval cell, in which to undergo 
its final changes to a chrysalis and perfect fly. This cell is 
formed of earth, but is lined and intermixed with liquid glue 
secreted in the stomach, and ejected by the mouth. This liquid 
glue is obviously nothing more than silk in a liquid state, 
—a preparation with which the larva of nearly every moth, 
