THE MYRIAPODA. 330 



four segments which follow the head are free, and their append- 

 ages resemble ordinary limbs. The anterior pair is turned 

 forward and comes into relation with the mouth, and the ter- 

 o-utn of the first somite is often enlarged ; of the other three 

 somites, the appendages of one appear to be always abortive. 

 Thus there are three segments with single pairs of legs. 

 The rest each bear two pairs. 



In the Chilopoda, on the contrary, the head is followed by 

 a basilar segment (Fig. 96, B), formed, according to Newport, 

 by the union of four embryonic somites, and carrying three 

 pairs of appendages. Of these the first are limb-like, but 

 are turned forward beneath the mouth (Fig. 96, D, vi') ; the 

 second pair are the strong recurved poison-claws, and the 

 hindermost pair may become functional legs, resembling those 

 which are attached to the succeeding somites, but are always 

 smaller than the others, and may be altogether aborted in the 

 adult. The somites of the body never bear more than one 

 pair of limbs. 



The alimentary canal is usually straight and simple, like 

 that of an insect larva. There are large salivary glands, and 

 the intestine is provided with Malpighian tubules. 



The heart extends through the greater part of the length 

 of the body, and is many-chambered, there being one cham- 

 ber for each of the somites in which it lies. Each chamber is 

 somewhat conical in shape, being broader behind than in front, 

 and admits the blood by a pair of lateral clefts, while the 

 blood leaves it, in part by the communication with the adja- 

 cent chamber, in part by lateral arterial branches. A medi- 

 an aortic trunk continues the heart forward, and the lateral 

 trunks encircle the oesophagus and unite into an artery which 

 lies upon the ganglionic chain. The arterial system in the 

 Chilopoda is, in fact, as complete as that of the Scorpions. 1 



The respiratory organs are trachea?, which open by stig- 

 mata on the lateral or ventral surface of more or fewer of the 

 somites. In Scutigera the stigmata are situated in the me- 

 dian dorsal line of the bodv. 



The nervous system presents a ventral chain, with a pair 

 of ganglionic enlargements for each segment of the body, the 

 most anterior of which are connected by commissures, which 

 embrace the oesophagus, with the cerebral ganglia. 



The ovary in both Chilognatha and Chilopoda is long, 



' Newport, " On the Structure, Relations, and Development of the Nervous 

 and Circulatory Systems in the Myriapoda and Macrurous Arachnida." (" Phi- 

 losophical Transactions," 1863.) 



