THE STUDY OF INSECTS. 
5S 
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, thorax, 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 
an appearance very different from that of 
the eye of higher animals; its surface 
a large number of six-sided divisions 
Fig. 72. — Part of com- 
f iour.d eye, greatly en- 
arged. 
is divided into 
