554 



CLASS II. ONYCHOPHORA. 



everywhere, except on the lips and one or two other places, 

 raised into minute secondary 'papillae or scales (Fig. 340) which 

 may be pointed or blunt ; eacli of them is in relation with 

 a subjacent epidermal cell in which the skin pigment is con- 

 tained. 



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. 333). 

 Within the buccal cavity are the two jaws. They are short, 



FIG. 334. Inner jaw-claw of P. FIG. 335. Outer jaw-claw of P. 



eapensis (after Balfour). capensis (after Balfour). 



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. 333). The tongue bears a row 

 of small chitinous teeth. The jaw-claws (Figs. 334 and 335), 

 which resemble in all essential points the claws borne by the 

 feet, and like these are thickenings of the cuticle, are sickle- 

 shaped. They have their convex edge directed forwards and 

 their concave or cutting edge turned backwards. The inner 

 cutting plate (Fig. 334) usually bears a number of cutting teeth 

 in addition to the main tooth. In some species the majority 

 of these are separated by a diastema from the others and 



