PART I. THE STRUCTURE AND 

 GROWTH OF INSECTS 



CHAPTER II 



INSECTS AND THEIR NEAR RELATIVES 



If we are to study insects, it is necessary that we should have a 

 clear conception of just what an insect is and how insects may be 

 distinguished from other animals. Most of us recognize bees, flies, 

 beetles, and butterflies as insects, but other forms of insect life we 



C 



FIG. i. Earthworm 

 m, mouth ; r, girdle, or clitellum. (After Jordan and Heath) 



' worms," 



and various insectlike animals are 



should probably call 

 commonly termed " insects." 



The animal kingdom is divided into two large groups of animals, 



- those having a backbone, the Vertebrates, and those without a 



backbone, the Invertebrates. In the former are included all the 



FIG. 2. Diagram to express the fundamental structure of an arthropod 



a, antenna ; a/, alimentary canal : b, brain : d, dorsal vessel ; ex, exoskeleton ; /, limb : 

 n, nerve chain : s. subesophageal ganglion. (After Schmeil, from Folsom) 



higher animals, such as the fishes, reptiles, birds, and mammals ; 

 while in the latter are included all the lower forms of life, which 

 are usually smaller in size and soft-bodied, as the molluscs, echino- 

 derms, worms, insects, and their relatives. 



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