2 THE LIFE OF CRUSTACEA 



In addition to those just mentioned, a few Crus- 

 tacea are sufficiently well known to be distinguished 

 by popular names, such, for example, as Crayfish 

 and Hermit Crabs, but for the vast majority no 

 names are available except those of technical 

 zoology. In the following pages, therefore, while 

 technical terms have been introduced as sparingly 

 as possible, the unfamiliarity of the animals them- 

 selves makes it needful to use many unfamiliar 

 names. 



In the classification of the Animal Kingdom, the 

 Crustacea form one of the divisions of a compre- 

 hensive group, or Phylum, known as Arthropoda. 

 The typical members of this group have a more or 

 less firm external skeleton, the body is divided into 

 segments, there are jointed limbs, and some of these 

 are modified to serve as jaws. The chief divisions 

 or classes of the Arthropoda are (i.) Insecta, in- 

 cluding Butterflies, Moths, Bees, Wasps, Flies, 

 Beetles, and the like ; (ii.) Chilopoda, or Centipedes ; 

 (iii.) Diplopoda, or Millipedes 1 ; (iv.) Onychophora, in- 

 cluding the curious worm-like Peripatus ; (v.) Arach- 

 nida, or Scorpions, Spiders, Mites, and their allies ; 

 and (vi.) Crustacea. 



It is not easy to summarize in a few words the 

 characters common to all Crustacea, and distinguish- 

 ing them from the other groups of Arthropoda. As 



1 The Chilopoda and Diplopoda are sometimes regarded as 

 forming a single class Myriopoda. 



