MTEIAPODA. 



515 



The head of the Myr^iapods corresponds closely with that of the 

 Insects, and, like the latter, bears a pair of antennae, the eyes, and 

 two or in the Chilopoda three pairs of jaws. The antennae are 

 placed on the frontal region, and are usually filiform or setiform. 

 The strongly-toothed mandibles resemble those 

 of Insects, and, like the latter, are without palps. 

 The maxillse in the Chilognatha have the form 

 of a complicated lobed oral valve (fig. 427 6), 

 the parts of which were formerly supposed to 

 represent two pairs of maxillae fused together ; 

 while in the Chilopoda they consist of a single 

 blade bearing a short palp (fig. 425). In rare 

 cases the mouth parts are transformed into a 

 suctorial apparatus (Polyzonium). 



The body is composed of similar and distinctly 

 separated segments, the number of which varies 

 considerably in different species, but is usually 

 constant for the same species. The segments 

 bear paired appendages, and a strong dorsal 

 and ventral plate (tergum and sternum) may 

 often be distinguished. Although the segments 

 of the body are so much alike that it is impos- 

 sible to fix a limit between thorax and abdomen, 

 still certain features of the internal organisation, 

 especially the fusion of the three first ganglia of the ventral chain, 

 show that we must regard the three anterior body segments at least 

 of the Chilognatha as constituting a thorax. In the Chilognatha 

 a single pair of legs is attached to each of the first three to five body 

 segments ; each of the following segments, on the other hand, heart 



FIG. 418. SoolopenSra 

 mortitans. 



FIG. 419. lulus terrestri* (after C. L. Koch). 



almost invariably two pairs, so that they may be regarded as double 

 segments, formed by the fusion of two somites. The legs may be 

 attached to the sides of the somites (Chilopoda), or nearer the middle 

 line of the ventral surface (Chilognatha), and are usually short with 

 from six to seven joints, and terminate with claws (figs. 418 and 419). 

 In their internal structure the Myriapods closely resemble the 



