CHAPTER II 



INSECT STRUCTURES 



5. Definition for an Insect. The characters of the 

 branch to which insects belong have been given. The 

 characters which are possessed by all insects are embraced 

 in the definition for an insect which is as follows: 



An insect is an Arthropod which has three distinct regions 

 to the body, the head, the thorax and the abdomen. It 

 bears, on the head, one pair of antennce or feelers, on the 



thorax, three pairs of legs, and, 

 usually, one or two pairs of 

 wings. 



6. The Head. The insect 

 body is made up of a variable 

 number of segments, but this 

 variation is always in the third 

 region or abdomen. The head 

 consists always of a single seg- 

 ment. This is made up of a 

 skull-like single piece to which 

 are attached the antennae and 

 the mouth parts and in which 

 are found the eyes. This skull 

 is called the epicranium. The 

 antennce are extremely varia- 

 ble. They are jointed but the number of joints ranges 

 from a single one to several hundred. They may be almost 

 too small to be seen or several times as long as the body. 



4 



FIG. 1. Head of Grasshop- 

 per, Front View. 



a, vertex; 6, compound eye; c, 

 ocellus; d, front; e, cheeks or 

 genae; /, clypeus; g, labrum; h, 

 edges of maxillae and labium; t, 

 mandibles. 



