CLASS OF THE MYEIAPODA. 411 



which have the mouth arranged for suction, and which do 

 not undergo a metamorphosis. As indicated by their name, 

 they live on the bodies of other animals, whose veins they 

 suck. They form two genera, the pediculus (Fig. 405) and the 

 ricusin ; these last attach themselves to the dog and to various 

 birds. 



548. Finally, the insects of the order thysanoura com- 

 mence equally with the form which they preserve through 

 life, and are always without wings ; but they are distinguished 

 from the preceding by their masticatory apparatus, and by 

 the appendages with which their abdomen is provided. These 

 are the podurellae (Fig. 352), the lepisma, machilis (Fig. 

 406), Ac. 



CLASS OF THE MYRIAPODA. 



549. The myriapoda respire air by means of tracheae, 

 like insects, but they differ considerably from these animals, 

 as well as from the arachnides, by their general conformation. 

 Not only they never have wings, but their body, much elon- 

 gated and divided into a great number of rings, carries on each 

 of these segments at least a pair of limbs, besides the number 

 of these organs, always twenty four at least, or more; nor is 

 there any line of demarcation between the thorax and the 

 abdomen. They somewhat resemble serpents, or worms with 

 feet ; but their internal organization brings them nearer to 

 ordinary insects, excepting that their circulatory system is 

 much less incomplete. 



The head of the myriapoda is provided with two small 

 antennae, and with two eyes, generally formed by the reunion 

 of ocelli. Their mouth is formed for mastication, and is pro- 

 vided with a pair of bi-articulated mandibles, followed by a 

 sort of lip with four divisions, and with two pairs of appen- 

 dages resembling little feet. The number of the rings of their 

 bodies varies, and sometimes these segments appear re-united, 

 two and two, in such a way that each moveable segment carries 

 two pairs of limbs (Fig. 407). These last organs terminate 

 only in a single hook. Finally, there exists on either side of 

 the body a series of stigmata, in communication with tracheae, 

 formed in the same way as those of ordinary insects. The 

 myriapoda experience metamorphoses in youth, but these 

 changes are not analogous to those we have seen take place 



