INTRODUCTION. 
f> 
o 
or reproductive form. Exceptional forms occur, but 
every insect must possess the following marks : “ It 
must breathe air, and have its body cut into (in-sected, 
hence the name) three distinct parts, possess, as a rule, 
six legs and two antennae;” if it be destitute of these 
characteristics the animal is not an insect properly 
so called. 
But let us try to learn something more definitely of 
the structure of an insect by examining the various 
parts of its organization. At present we are concerned 
only with the adult form, or imago as it is called. If 
you take an insect, and after having killed it you 
examine it, you will notice that its body is composed of 
distinct rings and segments, of a consistency more or 
less horny, that these rings are joined to each other by 
a membranous skin, which serves to give flexibility to 
the whole. This outward integument is rendered more 
or less hard by a deposit of chitine , which extends from 
the exterior into the interior ; in some insects, as in 
the horny wing-cases of beetles, this chitinous deposit 
is very thick, in others it is of softer texture, but is 
always sufficiently firm for the attachment of the 
muscles. Generally, thirteen rings or segments com¬ 
pose the body of an insect, there being one segment for 
the head, three for the thorax, and nine for the 
abdomen; but sometimes two or more are amalgamated 
together or concealed by others, so that fewer appear. 
We will now examine in detail the head, thorax, and 
abdomen. 
The head is formed of one single piece, and bears the 
antenme, the eyes, and the various organs of the mouth; 
the antennre vary much in form, sometimes they are 
B 2 
