MYKIAPODA. 157 



CHAPTEE XV. 



MYRIAPODA. 



Class III. Myriapoda. 



This class is a small one, and includes only the Centipedes and the 

 Millepedes. In all the Myriapoda the head is distinct, and not 

 amalgamated with the thorax. Tliere is no clear houndary-line 

 between the thorax and the abdotnen, both being composed of nearly 

 similar segments. The body (except in the genus Pauropiis) always 

 consists of more than twenty rings; and the hinder segments, which 

 correspond to the abdomen, always carry locomotive appendages, 

 whereas the abdominal rings in Arachnida and Insecta are always 

 destitute of locomotive appendages. One pair of antemnm is present, 

 and the number of the legs is always more than eight pairs. Respira- 

 tion is carried on by branched air-tubes or tracheae. 



In most of their characters the Myriapoda closely resemble the 

 true Insects, with which, indeed, they are not uncommonly classed. 

 The true Insects, however, always have the head, thorax, and abdo- 

 men distinct from each other, and have never more than three pairs 

 of legs. In most of the Myriapoda the young or " larvae " are more 

 like insects than the adult, since they have only three pairs of legs, 

 or are altogether destitute of feet. In some cases, however, the 

 young Myriapod, on escaping from the egg, possesses nearly all the 

 characters of the parents, except that the number of body-rings, 

 and consequently of legs, is smaller, and increases with every change 

 of skin ("moult"). The class is divided into two leading groups 

 or ordei-s, represented by the common Centipedes {ChUopoda) and 

 Millepedes {Chilognaiha). 



The Centipedes (fig. 105) are carnivorous in their habits, and the 

 organs of the mouth are adapted for a life of rapine. In addition to 

 the parts of the mouth proper, they have two pairs of " foot-jaws," 

 of which the second is hooked and perforated for the discharge of a 

 poisonous fluid. The bite of the common European species is per- 

 fectly harmless to man, but some of the tropical forms attain a 

 8 



