ARTHROPODA 105 



supported on many pairs (fourteen to forty-two, accord- 

 ing to the species) of short, fleshy appendages which 

 are not jointed. These animals are chiefly of interest 

 because of the fact that in certain features of structure, 

 as the size of the brain, the presence of tracheae, the 



FIG. 63. Perifatus ; natural size. 



arrangement of the circulatory system, and the clawed 

 appendages, and in their mode of development, they 

 resemble the Arthropods, while in other respects, espe- 

 cially as regards the excretory and nervous systems 

 they approach the Annulata and the Flatworms, Thus, 

 the class serves to connect the Arthropods and the 

 " Worms." 



CLASS 3. Myriapoda 



Myriapods are air-breathing Arthropods having the 

 body divided into similar segments, so that thorax and 

 abdomen are scarcely distinguishable. They resemble 

 worms in form and in the simplicity of their nervous 

 and circulatory systems ; but the skin is stiffened with 

 chitin, and the legs (indefinite in number) are articu- 

 lated. The legs resemble those of insects, and the 

 head appendages follow each other in the same order 

 as in insects eyes, antennae, mandibles, maxillae, and 

 labium. They breathe by tracheae, and have two 

 antennae and a pair of eyes. 



There are two important orders : 



i. Chilopoda, characterized by haying a flattened body 

 composed of about twenty segments, each carrying one 

 pair of legs, of which the hindermost is converted into 



