EXTERNAL FEATURES 



South African species the colour of the dorsal surface varies from 

 a dark green graduating to a bluish gray, to a brown vary- 

 ing to a red orange. The colour of the Australasian species 

 varies in like manner, while that of the Neotropical species (S. 

 American and W. Indian) is less variable. The skin is thrown 

 into a number of transverse ridges, along which wart-like papillae 

 are placed. The papillae, which are found everywhere, are specially 

 developed on the dorsal surface, less so on the ventral. Each 

 papilla carries at its extremity a well-marked spine. 



The appendages of the head are the antennae, the jaws and 

 the oral papillae. 



The antennae, which are prolongations of the dorso- lateral 

 parts of the head, are ringed, and taper slightly till near their 

 termination, where they are slightly enlarged. The rings bear a 

 number of spines, and the free end of the antennae is covered by 

 a cap of spiniferous tissue like that of the rings. 



The mouth is at the hinder end of a depression called the 

 buccal cavity, and is surrounded by an annular tumid lip, raised 

 into papilliform ridges and bearing a few spines (Fig. 3). Within 

 the buccal cavity are the two jaws. They are short, stump-like, 

 muscular structures, armed at their free extremities by a pair of 

 cutting blades or claws, and are placed one on each side of the 

 mouth. In the median line of the buccal cavity in front is 

 placed a thick muscular protuberance, which may be called 

 the tongue, though attached to 

 the dorsal instead of to the 

 ventral wall of the mouth (Fig. 

 3). The tongue bears a row of 

 small chitinous teeth. The jaw- 

 claws (Figs. 4 and 5 ), which re- 

 semble in all essential points 

 the claws borne by the feet, and 



like these are thickenings of the ^'^"eit "of?.^' m"- 



pensis. (After 

 Balfour.) 



Fia. 5. Outer jaw- 

 claw of P. ca- 

 pensis. (After 

 Balfour.) 



cuticle, are sickle-shaped. They 



have their convex edge directed 



forwards and their concave or cutting edge turned backwards. 



The inner cutting plate (Fig. 4) usually bears a nimiber of cutting 



teeth. The jaws appear to be used for tearing the food, to which 



the mouth adheres by means of the tumid suctorial lips. The 



oral papillae are placed at the.sides of the head (Fig. 3). The 



