2 ;6 ELEMENTARY ENTOMOLOGY 



of hardened plates. These plates are known as sclerites, and the 

 depression between two plates is called a suture. The hardness 

 of the plates is due to the deposition of a horny substance called 

 chitin. 



2. General divisions of the body. Typically the bodies of all 

 insects are divided into a series of rings, or segments. In many 

 places two or more of these rings have grown together, or are fused. 

 Again, in certain regions of the body, parts of the segments may be 

 lost. Regardless of the amount of variation in this respect, however, 

 we find that the segments are always grouped into three regions, 

 known as head, thorax, and abdomen. 



a. The head. The head is made up of a number of segments, 

 which are fused together, forming a boxlike structure. On the 

 head are found the eyes, mouth-parts, and antennae. 



b. The thorax. This is the second division of the body, and 

 consists of three segments, known as the prothorax (division nearest 

 the head), mesothorax, and metathorax. Each of these segments 

 bears a pair of walking appendages, and in addition the meso- 

 thorax and metathorax are provided with wings. 



c. The abdomen. This is the third division of the body, and is 

 made up of eleven segments. The posterior segments, however, 

 are not complete, showing modifications. 



Exercise 1. Pin the specimen to the bottom of a dissecting dish, spread the 

 wings and wing-covers of one side, and make an enlarged drawing (dorsal view) 

 of the entire insect, showing the above-named divisions. 



3. Detailed study of the head. As already noted, the head of the 

 locust is made up of a number of segments which have been firmly 

 fused together. The following divisions should be noticed : 



a. The epicranium. This is a boxlike piece which surrounds the 

 eyes and forms the basis of attachment for the movable parts of 

 the head. It extends down the front of the head, between the eyes, 

 to the transverse suture, and down the sides of the head to the 

 base of the mouth-parts. The sides of the epicranium below the 

 compound eyes are known as the genae, or cheeks, while the front 

 of the head between the compound eyes is called the frons. 



b. The compound eyes. These are situated upon the upper por- 

 tion of the sides of the head, and are large, brown, oval areas with 



