560 



CLASS H. ONYCHOPHORA. 



cor 



composed of a single layer of cells, which vary, however, a good 

 deal in size in different regions of the body. The cells excrete 

 the cuticle, and they stand in a very remarkable relation to the 

 secondary papillae of the cuticle just described. Each epidermis 

 cell is in fact placed within one of these secondary papillae, so 

 that the cuticle of each secondary papilla is the product of a 

 single epidermis cell. The pigment which gives the character- 

 istic colour to the skin is deposited in the protoplasm of the 

 outer ends of the cells in the form of small granules. 



At the apex of most, if not all, the primary wart-like papillae 



there are present oval aggre- 

 gations, or masses of epider- 

 mis cells, each such mass 

 being enclosed in a thickish 

 capsule and bearing a long 

 projecting spine. These 

 structures are probably 

 tactile organs. In certain 

 regions of the body they 

 are extremely numerous ; 

 more especially is this the 

 case in the antennae, lips, 

 and oral papillae. On the 

 ventral surface of the peri- 

 pheral rings of the thicker 

 sections of the legs they are 

 also very thickly set and 

 fused together so as to form 

 a kind of pad (Figs. 336 

 and 337). In the antennae 

 they are thickly set side by side on the rings of skin which 

 give such an arthropodan appearance to these organs in 

 Peripatus. 



The apertures of the tracheal system are placed in the depres- 

 sions between the papillae or ridges of the skin. Each of them 

 leads into a tube, which may be called the tracheal pit (Fig. 341), 

 the walls of which are formed of epithelial cells bounded towards 

 the lumen of the pit by a very delicate cuticular membrane con- 

 tinuous with the cuticle covering the surface of the body. The 

 pits vary somewhat in depth ; the pit figured was about 0'09 mm. 



-op n 



FlO. 340. Eye of Peripatus capensis as shown in 

 a longitudinal section through the head (partly 

 diagrammatic), cor Cornea ; / lens ; op optic 

 ganglion; op. n optic nerve : pi.r pigment : Re 

 retina ; sp secondary papillae of skin (after 

 Balfour). 



