138 STATES OF INSECTS. (Larva.) 
larva of the Hymenopterous tribe of saw-flies (Serrifera), 
in those of some Lepidoptera (Hepiolus, &c.), and in 
some few Coleopterous and Dipterous genera. Those 
of the former are of the shape of a truncated cone, and 
resemble the second class of unguiculate prolegs, except 
in the defect of claws. In the latter they are a mere re- 
tractile nipple-like protuberance, in some species so small 
as scarcely to be perceptible. In all they aid in progres- 
sive motion ; but it is by laying hold of surfaces, and so 
enabling the body more readily to push itself forward 
by annular contraction and dilatation, and not by taking 
steps, of which all prolegs are incapable: to assist in this 
purpose the protuberance sometimes secretes a gluten, 
which supplies the place of claws. Some larve have the 
power of voluntarily dilating certain portions of the un- 
derside of their body, so as to assume nearly the shape 
and to perform the functions of prolegs. In a Coleopte- 
rous (?) subcortical one from Brazil, before alluded to, 
there are four round and nearly flat areas in each ventral 
segment of the abdomen, but the last very little raised 
above the surface, and rough, somewhat like a file; and 
besides these, the base of the anal segment has ten of 
these little rough spaces, but of a different shape, being 
nearly linear, placed in a double series, five on each side. 
Doubtless these may be regarded as a kind of prolegs, 
which enable the animal to push itself along between the 
bark and the wood °. 
In considering, in the next place, the number and 
situation of the prolegs, it will contribute to distinctness 
to advert to these circumstances as they occur in the dif- 
ferent orders furnished with these organs. 
To begin with the Lepidoptera.—Lepidopterous larvee 
* De Geer v. 203. ® See above, p. 110, 114. 
