CLASSIFICATION 107 



finally scientists often name species of animals after some one 

 who has become an authority in the subject; for example, one 

 of our common hawks was named Buteo swainsoni in honor of 

 the bird student Swainson. 



Classification of Insects. - - It would seem as though the value 

 of our system of classification could be thoroughly tested by 

 means of the insects, since this group of about four hundred 

 thousand known species of animals constitutes a single class, 

 the Insecta. The class Insecta is included in the phylum Arthro- 

 poda along with three other classes, the Crustacea (crayfish, 

 lobster, etc.), Myriapoda (thousand-legged worms, etc.), and 

 Arachnida (spiders, mites, etc.). These classes are also larger 

 than most other classes in the animal kingdom, and hence the 

 arrangement of the members of this one phylum Arthropoda 

 might be expected to be rather difficult. But while it is true 

 that we still do not know exactly where a few of the arthropods 

 belong, most of them fit into their places without difficulty. 



CHARACTERISTICS or THE CLASS INSECTA. -- The members of 

 the class Insecta are characterized by the presence of one pair of 

 antennae, three pairs of legs, and usually wings. The crayfish is 

 not an insect, for it has two pairs of antennae, five pairs of legs, 

 and no wings. The spiders are not insects since they have four 

 pairs of legs and no antennae, and the thousand-legged worms 

 are not insects because they have a great many pairs of legs and 

 no wings. All of these animals belong to the phylum Arthro- 

 poda, however, because they have an outer covering or exoskele- 

 ton of chitin instead of a backbone, have a body divided more 

 or less distinctly into similar parts (segments) arranged in a 

 linear series, and possess paired, jointed appendages (legs, etc.) 

 on some or all of the segments. 



ORDERS OF INSECTS. - - Insects have been divided into eight 

 orders according to (i) the presence or absence of wings, and 

 their number and structure when present, (2) the structure of 

 the mouth parts (biting or sucking), and (3) the character of 

 the metamorphosis. Although some of the orders would have 



