AN INTRODUCTION TO ENTOMOLOGY 



CHAPTER I. 



THE CHARACTERS AND METAMORPHOSES OF INSECTS 

 (HEXAPODA). 



I. THE CHARACTERS OF THE HEXAPODA. 



THE term Insect is from two Latin words in, in, and seco, to cut. 

 It refers to the fact that in the animals indicated by it the body is 

 divided by transverse incisions into a series of segments. As has 

 been shown in the Introductory Chapter, this insected form of the 

 body is characteristic of two of the larger divisions of the Animal 

 Kingdom, the Vermes, or Worms and the Arthropoda. But the term 

 Insect has become restricted to a portion of this great series of ani- 

 mals. There is, however, a lack of uniformity in the use of the term 

 among zoological writers. By some it is applied to all Arthropoda 

 that breathe by means of a system of air-tubes (tracheae) extending 

 throughout the body. This includes Centipedes, Millepedes, Spiders 

 and allied forms, as well as the six-footed insects. Other writers in- 

 clude among Insects only those orders which are characterized by 

 the possession of but six legs. It is in this restricted sense that I 

 have used the term Insect. Whenever reference is made to all of the 

 Arthropoda that breathe by means of tracheae, they are designated 

 as the Trachedta. 



Insects, in the restricted sense indicated above, constitute the 

 class HEXAPODA.* The insected or 

 segmented form of the body is shown 

 in Fig. i, and in nearly all of the 

 species figured in the following pages. 

 The peculiar structure of the respira- 

 tory system, which is characteristic of 

 these animals, and which allies them 

 to other Tracheata, is described in the next chapter. In the Hexapoda 



FlG> I( _ Nymph of the Red . le{rg ed Locust. 

 (After Emenon > 



*Hexapoda : hex (e%), six; pous (itovS), a foot. 



