x PHYLUM ARTHROPODA 239 



Each /aw is composed of two curved, falciform, chitinous plates; they 

 lie at the sides of the mouth enclosed by a circular lip. The jaws, as 

 well as the oral papilla;, are developed as modified limbs. The legs are 

 not jointed; each consists of a proximal part and a small distal part or 

 foot, terminating in a pair of horny claws. 



In the internal anatomy (Fig. 139) the most important features are the 

 presence of organs of respiration in the form of tracheae, unbranched or 

 little branched tubes, groups of which open on little depressions of the 

 integument, the external openings or stigmata of which are in some 

 species distributed irregularly over the surface, in others arranged in 

 longitudinal rows; the presence of a series of pairs of nephridia {nepli) 

 similar to those of the Annulata, and of a nervous system consisting 

 of a brain (brn), situated in the head, and two widely separate nerve 

 cords (ne. co) which run parallel with one another throughout the 

 length of the body, and are not dilated into distinct ganglia. The 

 sexes are distinct. 



The various species of Peripatus are all terrestrial, and are found in 

 damp localities under bark, or dead timber, or stones. Four species 

 occur in South Africa, one in South America, and one in the West 

 Indies, one in New Zealand, and two in Australia. 



3. THE MYRIAPODA 



The class Myriapoda, including the centipedes and the 

 millipedes, consists of tracheate Arthropoda, which bear 

 many features of resemblance to the insects. There is a 

 distinct head, bearing a single pair of many-jointed antennae, 

 a pair of eyes, and from two to four pairs of jaws ; and a 

 trunk, not distinguishable into regions, but consisting of 

 a number of similar segments, each bearing either one pair 

 of legs or two. A system of air-tubes or tracheae similar to 

 those of Peripatus or the insects open by a series of stigmata 

 (in centipedes on alternate segments) on the sides or lower 

 surfaces of the segments. 



The head in the Myriapoda (Fig. 140) is as well marked 

 off as in an insect ; it appears to be composed of about four 



