282 



THE INVERTEBRATA 



linked with the environment in which they lurk away from light and 

 enemies. Yet it can hardly be doubted that the Onychophora are a 

 division of the Arthropoda which has preserved more primitive 

 features of an ancestral race than any other living forms, terrestrial 



Fig. 203. Peripatus capensis, x very slightly. From Sedgwick. 



or aquatic. Such features are in all probability the thin cuticle, the 

 muscular body wall, the annelid-like eye, the small number of head 

 segments, the complete series of segmental excretory organs, the 

 presence of cilia and possibly also the parapodia-like limbs. 



The thinness of the cuticle is responsible for the absence of external 

 segmentation (save for the repetition of the appendages). The head 

 (Fig. 204) bears three pairs of appendages which are none of them 



Fig. 204. Peripatus capensis, ^ . Ventral view of anterior end. a7it. pre- 

 antenna; o.p. oral papilla ;y. jaw; i, first trunk appendage. After Sedgwick. 



very highly developed. While elsewhere in the arthropods the first 

 segment is present in the embryo but disappears in the adult, here it 

 persists and bears a pair of appendages which maybe called preantennae 

 (to distinguish them from antennae). They are rather long and very 

 mobile, but not retractile like the tentacles of the slug. The next seg- 

 ment bears the jaws, which are not unlike enlarged claws of the trunk 

 appendages and bite with the tip and not the side. They are moreover 

 tucked within the oral cavity. But they are borne on muscular 



