DESCRIPTION OF PERIPATUS. 251 



but scorpions have " lung-books," and most spiders have both 

 lung-books and tracheae, while the king-crab has " gill-books." 

 Except the mouth-parts of Insects, the appendages are 

 not forked like those of Crustaceans. 



First Class of Tracheata — Protracheata, including one 

 genus, Peripatus. 



General Characters of Protracheata. 



The body is in form like that of a worm or caterpillar, 

 soft-skinned, and without external segmentation. 



There is a pair of prominent pre-oral antennae. 



The true appendages are — a pair of jaws in the mouth, 

 a pair of slime-secreting oral papillae, numerous pairs of 

 short, imperfectly jointed legs with two claws apiece, and a 

 pair of anal papillae. The legs contain peculiar (coxal) glands. 



Respiration is effected by numerous tracheae, whose open- 

 ings are somewhat scattered on the surface of the body. 

 The heart is simply an elongated dorsal vessel with valvular 

 openings. There is a series of excretory tubes or nephridia. 

 The halves of the ventral nerve-cord are widely separate. 



The single genus Peripatus is represented by numerous 

 (twelve) species, widely distributed; in its possession of trachese 

 and nephridia it is an interesting connecting link; in many ways 

 it seems to be an old-fashioned survivor of an archaic type. 



The species of Peripatus are beautiful animals. fcJedg- 

 wick says — ■" The exquisite sensitiveness and continually 

 changing form of the antennae, the well-rounded plump body, 

 the eyes set like small diamonds on the side of the head, the 

 delicate feet, and, above all, the rich colouring and velvety 

 texture of the skin, all combine to give these animals an 

 aspect of quite exceptional beauty." As to their habits, 

 Hatchett Jackson says — " They live under stones, in rotting 

 wood, etc., in moist places, are nocturnal in habit, and feed 

 on insects, etc., which they ensnare by the ejection of slime 

 from the oral papillae." To their shy habits, their persist- 

 ence is possibly in part due. They are able to move 

 quickly, somewhat after the fashion of Millipedes, especially 

 like Scolopendrella. Young forms roll up when touched, 

 and have been seen to climb up vertical glass plates. 



