392 
CLASS VIIT. 
moreover, there may be distinguished in it two short conical an- 
tennz, two strong mandibles, two maxille with small palps, and an 
under-lip, which also has two small palps and terminates in a point, 
under which the efferent canal of the matter with which the cater- 
pillar prepares its web is situated. This substance is secreted as a 
fluid by two long, blind, convoluted vessels, which lie at the sides 
of the intestinal canal. Most caterpillars live on vegetable food, 
especially leaves, and many are limited to a single species of vege- 
table. Others, however, eat leather, fur, fat, wax, &c., and these 
belong especially to the family of the moths. Caterpillars usually 
change the skin four or five times before turning into pupe. 
The pupx of scaly-winged insects are quiescent, and move their 
abdomen alone when they are touched. They are oblong-ovate, and 
covered with a horny skin (pupe obtec'e, see above, p. 273). The 
pup of day-butterflies are usually not inclosed in a web, but merely 
attached by some threads at their posterior extremity, and hang 
freely with the head downward, or are fixed transversely to a branch, 
or other object, by a transverse band, as if in a hoop. The pup 
of nocturnal butterflies either lie underground in a cavity that is 
smooth and even within, and lined with web, or they are inclosed 
in a cocoon (folliculus), which is fastened to a branch, or to a wall. 
The web is frequently silken, sometimes very closely woven, some- 
times loosely ; sometimes it consists in part of finely gnawed fibres 
of wood interwoven with the threads of web, or of other foreign 
objects intermixed with the web, crumbs of earth, morsels of leaves, 
&e. These pups have commonly a brown or black colour. 
From the pupa of many species, especially of day-butterflies, the 
perfect insect proceeds after the lapse of a few days. Of such 
species there are ordinarily two generations in a year. Of other 
species, however, the caterpillar or the pupa remains through the 
winter, and then the perfect insect usually appears only once in the 
year, in spring or in summer. Eggs that are laid in autumn are 
mostly hatched in the following spring. 
The intestinal canal of caterpillars is straight, and consists in 
great measure of a wide cylindrical stomach. There are four very 
long vessels for secretion of urine. The perfect insect has a narrow 
c:sophagus with a lateral expansion or crop (the so-called sucking 
bladder, see above, p. 310); the stomach has become shorter, the 
rest of the intestinal canal longer. Lepidopterous insects in the 
perfect state of butterflies either take no food at all, or suck the 
