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 ; each 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 

 tmccal 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. FlG. 335. Outer jaw-claw of P. 



capensis (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 



