THE STUDY OF INSECTS. 



The subject of external anatomy of insects consists very 

 largely in a study of the sclerites of which the different 

 segments of the body and of its appendages are composed. 

 This part of the subject is quite difficult, and will not be 

 discussed here. It is treated, however, in the discussion of 

 the characters used in the classification of the Coleoptera 

 given on pages 499 to 504. These pages should be carefully 

 studied before attempting to use the table that follows them. 



FIG. 70. Side-view of Locust with wings 

 removed 



FIG. 71. Wasp, with 

 head, thora.x, and 

 abdomen separated. 



The segments of the body in a fully developed insect are 

 grouped into three regions : head, thorax, and abdomen 

 (Fig. 71). In the larval state this grouping of the segments 

 is not well shown. 



The Head and its Appendages. 



The head is the first of the three regions of the body. 

 It is supposed to be formed of several body-segments grown 

 together ; but entomologists differ in their views as to the 

 number of segments that have entered into its composition. 

 The head bears the compound eyes, the simple eyes, the 

 antennae, and the mouth-parts. 



The Compound Eyes. On each side of 

 the head of an adult insect is an organ, 

 which is recognized at once as an eye. 

 But when one of these eyes is examined 

 with a microscope it is found to present 



FIG. 72. Part of com- ,.,-, , , f 



pound eye, greatly en- an appearance very ditlerent trom that of 



the eye of higher animals ; its surface 



is divided into a large number of six-sided divisions 



