THE CRAYFISH AND ARTHROPODS IN GENERAL 



227 



III. MYRIAPODA 



FIG. 122. A millipede. (From Shipley and MacBride after Koch.) 



The myriopods are also annelid-like in appearance. The two 

 principal orders are the Chilopoda and Diplopoda. The Chilo- 

 poda or centipedes (Fig. 121) are flattened dorso-ventrally, have 

 one pair of legs at- 

 tached to every seg- 

 ment back of the 

 head, and possess a 

 pair of poison claws 

 attached to the first 

 segment. The Diplo- 

 poda or Millipedes ,. CR 

 (Fig. 122) are cylin- 

 drical, have two pairs 

 of legs attached to 

 every segment back 

 of the fourth, and 

 lack poison claws. 



The insects consti- 

 tute about four fifths 

 of all the species of 

 animals. The num- 

 ber of individuals is 

 even more remarka- 

 ble. The body of an 

 insect is divided into 

 head, thorax, and ab- FlG . I2 , t Diagr ' am to show the affinities of 

 domen. The thorax arthropods. 



PRIMITIVE ARTHROPODS 



