138 A COURSE ON ZOOLOGY. 



without undergoing metamorphosis, which is not the case 

 with all crustaceans. The spring or rock lobster, for 

 example, passes through metamorphoses. Before ar- 

 riving at adult size, the crayfish, crab, and lobster moult 

 a number of times, at least thirty. During all this 

 time the animal does not change in form ; it simply 

 grows larger. While without a hard shell the creature 

 is perfectly helpless, and lies hidden in some crevice. 



CHAPTER XV. 

 The Beetle. 



As a representative of the great division of insects, we 

 select one that is known throughout the whole world, 

 and which is far too abundant in many agricultural coun- 

 tries. It is the cockchafer ; but almost any beetle would 

 answer as well. 



When we examine a beetle we at once notice that the 

 animal as a whole is made up of three distinct parts, 

 head, thorax, and abdomen. Each of these parts is en- 

 closed in an envelope, consisting of hard, horny sub- 

 stance that forms the external skeleton ; under this 

 envelope are attached the muscles, and within it are sus- 

 tained and protected the soft parts. It is composed of a 

 series of strong rings, joined together edge to edge by 

 the intervention of a more flexible membrane that allows 

 a certain amount of motion. The arrangement of these 

 rings is easily seen on the abdomen of the beetle ; in 

 other parts, as the head and thorax, it is less marked. 

 It may, however, be noticed, and the same applies to all 



