INSECTS. 
513 
of a cornea, which is divided into a multitude of small facets; 
others have simple eyes, the cornea consisting of a single piece. 
The mouth of insects with six feet, is generally composed of 
six pieces, four of which are lateral, and disposed in pairs ; the 
other two are opposed to each other, and placed in a contrary 
direction. 
In sucking insects, or those which subsist on fluid aliment, 
there are two modifications of form in the lips. In one of 
these, they consist of small laminae, formed like lancets ; and 
by their union, become a kind of sucker, which is received 
into a cylindrical or conical sheath, articulated in the form of 
a beak. 
The trunk or thorax, is the part of the body next the head, 
and to which the feet are attached. It is composed of three 
segments, varying in their relative position. The hind part of 
the body, which is posterior to the thorax, is termed the abdo¬ 
men. This part contains the viscera, and the sexual organs, 
and consists generally of nine or ten segments, some of which, 
however, are frequently concealed, or greatly shortened. 
The greater number of insects undergo several metamorpho¬ 
ses : first the egg, which bursting, presents the caterpillar; and 
after it has lived its allotted time, becomes an aurelia, or chry¬ 
salis ; and then undergoes its final change into the perfect in¬ 
sect. A few, however, are not subject to a complete meta¬ 
morphosis. 
The limits of this little work will not permit a complete de« 
velopement of this numerous class, and we therefore propose 
giving an outline only of the eleven orders and principal tribes, 
and an illustration of the most striking genera of Latreille, 
whose arrangement we follow. 
ORDER I—THYSANOURA. 
Apterous insects with six feet, and not undergoing any trans¬ 
formation ; head distinct; two antenme, which are longer than 
the head; abdomen terminated by filaments on a forked tail. 
TRIBE I.-LEPISMEN/E. 
The antenme divided from their base into a number of small 
