GUIDE TO THE STUDY OF INSECTS. 



THE CLASS OF INSECTS. 



That branch of the Animal Khigdom known as the Ar- 

 THKOPODA, includes all animals having the body composed of 

 rings or segments, like short cylinders, which are placed suc- 

 cessively one behind the other, and which bear jointed appen- 

 dages, or feet. The plan of their entire organization, the es- 

 sential features which separate them from all other animals, 

 lies in the idea of articulation, the apparent joining together 

 of distinct body-segments, bearing hard, jointed appendages. 

 If we observe carefully the body of a Worm, we shall see that 

 it consists of a long cylindrical sac, which at regular intervals 

 is folded in upon itself, thus giving a ringed (annulated, or 

 articulated) appeai-ance to the body. In Crustaceans (crabs, 

 lobsters, etc.) and in Insects, from the deposition in the 

 skin of the latter of a peculiar chemical substance 

 called chitine, the walls of the body become so hard- 

 ened, that when the animal is dead and dry, it readily 

 breaks into numerous very perfect rings. 



Though this branch contains a far greater number of 

 species than any other of the animal kingdom, its myr- 

 iad forms can all be reduced to a simple, ideal, typical 

 figure ; that of a long slender cylinder, divided into 

 numerous segments, arranged in two or, as in Insects, 

 into three regions, and bearing jointed appendages. It Fig. i. 

 is by the unequal development and the various modes of group- 

 ing the rings, as well as the differences in their number, and also 

 in the changes of form of their appendages, i.e., the feet, jaws, 

 and antennfe, that the various forms of Arthropoda are pro- 

 duced. The Cuvierian branch Ariiculata comprise the modern 

 branches of Worms and Arthropods. 



Fig. 1. Worm-like larva of a Fly, Scenopimts.— Origina'. 

 1 



