INTRODUCTION. 
71 
by a small hole, through which issues the silken thread 
which serves so many important purposes in the re- 
markable changes these creatures undergo. This 
organ has been named the spinneret. On each side 
of the under lip, and connected with it at the base, 
are two minute palpiform bodies (e, e ), which may 
be regarded as the labial palpi. 
The efficiency of the organs just described, is well 
evinced by the address and rapidity with which these 
creatures consume the leaves which they select for 
their food. They invariably begin to gnaw the margin 
of the leaf, placing the body in such a position that 
a portion of the edge passes between the anterior 
legs, which support and keep it steady. Before ap- 
plying its mouth, the caterpillar stretches its body, 
and advances its head as far as possible, that it may 
command a larger extent of the leaf. The mandibles 
are moved with great rapidity, and every time they 
meet cut off a small piece, which is instantly swal- 
lowed. At every motion of the jaws, the head is 
drawn nearer the legs, and after it has been brought 
as far as possible, the body being contracted for the 
purpose, it is again extended to the point where it 
commenced to gnaw, and the same process repeated. 
In this manner the mandibles describe a succession 
of arcs, and the leaf is cut in the segment of a circle, 
somewhat resembling the circular incision made by 
the leaf-cutting bees. It seems, also, that the notch 
in the middle of the upper lip, formerly alluded to, 
is of great service, as it is placed on a line with the 
