CHAPTER I 



THE CHARACTERISTICS OF INSECTS AND OF THEIR 

 NEAR RELATIVES 



PHYLUM ARTHROPODA 

 The Arthropods 



IF an insect, a scorpion, a centipede, or a lobster be examined, 

 the body will be found to be composed of a series of more or less 

 similar rings or segments joined together; and some of these seg- 

 ments will be found to bear jointed legs (Fig. i) . All animals possess- 

 ing these characteristics are classed together 

 as the Arthropoda, one of the chief divisions or 

 phyla of the animal kingdom. 



A similar segmented form of body is found 

 among worms; but these are distinguished 

 from the Arthropoda by the absence of legs. 

 It should be remembered that many animals 

 commonly called worms, as the tomato-worm, 

 the cabbage-worm, and others, are not true 

 worms, but are the larvae of insects (Fig. 2). 

 The angle-worm is the most familiar example 

 of a true worm. 



In the case of certain arthropods the dis- 

 tinctive characteristics of the phylum are 

 not evident from a cursory examination. 

 This may be due to a very generalized condi- 

 tion, as perhaps is true of Peripatus; but in 

 Fig. i. An arthropod, most instances it is due to "a secondary modifi- 

 cation of form, the result of adaptation to 

 special modes of life. Thus the segmentation of the body may be 



Fig. 2. A larva of an insect. 

 (1) 



