556 CLASS II. ONYCHOPHORA. 



four (rarely more) papillae. The part of the foot which carries 

 the claws is especially retractile, and is generally found more or 

 less telescoped into the proximal part. The legs of the fourth 

 and fifth pairs differ from the others in the fact that the enlarged 

 nephridia of these segments open upon, or in close relation with 

 the proximal spiniferous pad. 



In some species certain of the legs bear on their ventral sides 

 furrows with tumid lips and lined by smooth non-tuberculate 

 epithelium ; they are called coxal organs. In some forms 

 (S. African, etc.) they are very faintly indicated ; in others 

 (neotropical, etc.) they are considerably deepened to form the 

 so-called coxal vesicles, which, it is stated, can be everted. 



The males are generally rather smaller and less numerous 

 than the females. In those species in which the number of legs 

 varies, the male has a smaller number of legs than the female. 



The slime glands open at the end of the oral papillae and are 

 contained in the central compartment of the body-cavity in 

 which they form conspicuous objects. Their ducts are con- 

 siderably dilated to form the large slime-reservoirs (Fig. 338 sl.d), 

 and the gland itself is tubular (aZ.gr), the tubes branching off 

 from the posterior end of the duct. The slime is a viscid, 

 albuminous fluid which hardens into threads in the air. Though 

 non-acrid and harmless, it adheres to all objects which it touches 

 except the skin of the animal itself. Its ejection is caused by 

 the contraction of the muscular body-wall of the animal and it 

 can be shot out to a considerable distance. It is used to entangle 

 the more active prey, but it has to be used sparingly, for after 

 a few ejections the supply stored in the reservoirs is exhausted. 



The Alimentary Canal (Fig. 338). The buccal cavity, as 

 explained above, is a secondary formation around the true mouth, 

 which is at its dorsal posterior end. It contains the tongue and 

 the jaws, which have already been described, and into the hind 

 end of it there open ventrally by a median opening the salivary 

 glands (s.g). The mouth leads into a muscular pharynx (ph), 

 which is connected by a short oesophagus (oe) with a stomach 

 (st). The stomach forms by far the largest part of the alimentary 

 canal. It is a dilated soft-walled tube, and leads behind into 

 the short rectum (R), which is slightly curved and opens at the 

 anus. There are no glands opening into the alimentary canal. 



The salivary glands, which open into the buccal cavity, are 



