XI 



PHYLUM ARTHROPODA 



593 



imperfectly cut off from the general body-cavity by a longitudinal 



partition. 



The organs of respiration (Fig. 489) are delicate, unbranched 



or rarely branched, tracheal tubes, lined with a thin chitinous layer 



exhibiting fine transverse striations. Groups of these open in 



little depressions of the integu- 

 ment, the tracheal pits (tr.p.), the 

 external openings of which are 

 known as the stigmata (tr.o.). 

 The stigmata are usually distri- 

 buted irregularly over the surface, 

 with a tendency to arrangement 

 in rows in P. capensis. By 

 means of these tubes air is con- 

 veyed to all parts of the body. 



A series of pairs of glands, the 

 coxal or crural glands (Fig. 488, 

 cox. gld.), lie in the lateral com- 

 partments of the body-cavity, and 

 their ducts open on the lower 

 surfaces of the legs just outside 

 the nephridial apertures. They 

 are absent in the female except 



-tr.o. 



Cin 



FIG. 488. Dorsal view of the internal organs FiQ. 489. Section through a tracheal pit 



of Peripatua. an. anus ; ant. antennae ; and diverging bundles of tracheal tubes 



brn. brain ; cox. gld. coxal gland of the seven- of Peripatus. tr. tracheae; tr. c. cells 



teenth leg ; S gen. male genital aperture ; in walls of tracheae ; tr. o. tracheal stigma ; 



ne. co. nerve-cord ; neph. nephridia ; or. tr. p. tracheal pit. (From Camb. Nat. Hist., 



pap. oral papillae ; phar. pharynx ; sal. gld. after Balf our.) 

 salivary gland ; si. gld. slime gland ; stom. 

 stomach. (Combined from Balf our.) 



in P. capensis, and their number and arrangement differ in the 

 males of the various species. Also opening on the ventral surfaces 

 of the legs are a series of thin-walled vesicles the coxal organs : 

 these occur in both sexes and are capable of eversion and retraction. 

 A pair of large glands the slime-glands (si. gld.) opening at 



