ELEMENTARY ENTOMOLOGY 



The Invertebrata are divided into several branches, or phyla (sin- 

 gular, phylum), which divisions are based on fundamental differences 

 in the body structure of the animals in these groups. Of these 

 phyla there are two which have the body made up of a series of 

 segments and were at one time classed together as the Articulata. 



FIG. 3. A lobster; a typical crustacean 



The first of these two phyla, the Vermes, or worms, has no jointed 

 appendages, while the second, the Arthropoda, is characterized by 

 having jointed appendages on either several or all segments of the 

 body, from which the term "Arthropoda," from art/iron (joint) 

 and pous (foot), is derived. The Arthropoda include the insects, 

 spiders, myriapods, and crustaceans, all of which are related by the 

 possession of these jointed appendages. The distinctions between 



