INTRODUCTION. 3 



or reproductive form. Exceptional forms occur, but 

 every insect must possess the following marks : "It 

 must breathe air, and have its body cut into {iii-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 chitlne, 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 suihciently 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 

 antennae, the eyes, and the various organs of the mouth; 

 the antennae vary much in form, sometimes they are 



B 2 



