56 



MYRIAPODA 



these two figures (Figs. 34 and 18) will show the position of the 

 organs mentioned in this account. The heart is shown with 

 the suspensory and alary muscles attached. 



Eec.sen 



ori.Act, 



Fig. 34. — Transverse section through Polyxenus lagimts : g.n.c, f.n.c, ganglionic and 

 fitrous parts of nerve cord ; Rec.sen, receptaculum seminis ; ori.dci, oviduct ; 

 Sjmizoa, spermatoza. (From Heathcole, Anatomy of PoZj-tojmm Za^Knis. ) , 



Order II. Chilopoda. 



The shape of the body differs from that of the Order which 

 has been just described (Chilognatha), inasmuch as it is not 

 cylmdiical but flattened, the back, however, being more arched 

 than the ventral sm-face. In this respect, however, it cannot be 

 said to differ from the other Orders which we have yet to describe. 



The segments are not formed hj a single ring of the 

 exoskeleton, which in this Order is formed of chitin, and is tough 

 and flexible rather than hard and strong ; but of two or three 

 plates which form a covering to the segment. The back is 

 covered by a large plate known as the tergum, the sides by two 

 plates known as pleura, and the ventral part by a plate called 

 the sternum. The pleura and sternum are, however, in most cases 

 fused together or indistinguishable. In this, as in most of the 

 anatomical peculiarities, there is a much greater difference 

 between the two Orders Chilopoda and Chilognatha than between 



