COLEOPTEEA OF INDIANA. 



THE EXTERNAL ANATOMY OF A BEETLE. 



Having thus seen that a beetle belongs to the class Insecta, it is 

 thought best, before giving its relation to the other orders of that 

 class, to describe brietiy the external parts of a typical specimen. 

 The beginner may thus the more 

 readily grasp the name and loca- 

 tion of the parts used in classifica- 

 tion, as well as the meaning of 

 many of the technical terms which, 

 of necessity, have to be used in such 

 a paper. The three regions of the 

 body, the head, the thorax and the 

 abdomen, will therefore be consid- 

 ered in order. 



The Head and Its Appendages. 



The front part of the body, the 

 head, is composed of three or more 

 rings or segments, completely fused 

 or compacted into a single hard boj 

 or cavity called the epicranium. 

 This contains the brain and acces- 

 sory ganglia, the mouth cavity and 

 the muscles moving the mandibles, 

 antennas and other sense organs 

 borne on the outer surface. 



The heads of beetles vary great- 

 ly in shape and size, and are joined 

 by a membrane to the thorax. Usu- 

 ally the portion behind the eyes is 

 more or less constricted into a neck, 

 which may be very long and nar- 

 row, or short and partly or wholly 

 immersed in the thorax. The up- 

 per part of the head is divided into 

 three regions, the back part being 

 called the occiput, the middle part 

 behind the eyes the vertex, while 

 the frontal portion, as far down as a more or less prominent trans- 

 verse suture between or in front of the antennse, is called the front. 

 This suture is known as the elypcal or frontal suture, and its pres- 

 ence or absence, position, depth, etc., is often used in classification. 



Fig. 1. Under surface and head from 

 above of beetle (Harpalus calighiosus) show- 

 ing the different parts. (After Smith.) 



