88 ZOOLOGY. 
active in insects; and they display, in general, an extraordinary degree 
of activity and muscular energy. The flight of many kinds is far more 
rapid, in proportion to their size, than that of birds; others display a 
similar superiority in running, swimming, and digging or burrowing ; 
whilst the leaping of many, as fleas and grasshoppers, and the springing 
of others, as cheese-hoppers, greatly exceed that of which any vertebrate 
animal is capable. : 
Insects feed on very different kinds of food. Some prey on other 
insects ; some devour animal, and some vegetable substances ; some suck 
the juices of animals, some the juices of plants or the honey of their 
flowers. The mouth of many is adapted for gnawing, cutting, or 
tearing ; that of others, for sucking. An insect’s mouth of the former 
kind is very complex in structure; and although the mouth adapted 
for sucking is apparently much more simple, it in reality consists of the 
same parts, but very much modified and united. The eyes of insects are 
of two kinds—simple and compound. Some have simple eyes only, others 
have only compound eyes; but the greater number have two large 
compound eyes on the sides of the head, and three small simple eyes 
between them. A compound eye is an 
organ of most remarkable structure. 
When examined through the micro- 
scope, its surface is seen to be divided 
into a great number of hexagonal 
facets, which are in fact cornew. In 
the ant, there are only about fifty 
of these facets in each eye ; but in the 
common house-fly, there are about four 
thousand, in butterflies, upwards of 
seventeen thousand, and in some 
beetles, more than twenty-five thou- 
sand. Each cornea may be regarded 
as belonging to a distinct eye, provided 

Fig. 68.—Section of the Eye of a 
Cockchafer (highly magnified) : 
A, section: a, optic ganglion into which ; : 
"the optic nerve swells; }, nerves arising and pupil of its own. The eyes of 
trom its surface, and proceeding to the ; : 
general retina: ¢, general retina; d, 1sects cannot be turned to one side, 
layer of pigment, in front of the general like those of vertebrate animals, and 
retina; e, optic nerves of the individual : 
eyes which form the compound eye. B, for the want of this power, compensa- 
a group of these, much magnified: f, bulb 4; 5 : : 
of optic nerve; g, layer of pigment; ii, tion is made by the number of eyes, 
vitreous humour ; #, cornea. each looking in its own particular 
direction. 
Insects, in general, take no care of their eggs after depositing them ; 
but they are guided by wonderful instincts to select the proper situa- 
tions for the deposition of them, so that the young, when hatched, may 
with a nervous apparatus, lens, iris, 
