CHAP. VI 



PROTRACHEATA 



427 



CLASS I. The Protraeheata (Onyehophora). 



An accurate knowledge of the organisation of the only genus belong- 

 ing to this division, Peripatus, is of the greatest importance, because it 

 combines unmistakable Annelid with unmistakable Tracheatan char- 

 acteristics. Of all living Arthropoda, Peripatus has perhaps best 

 preserved the original organisation of the ancestors of the Traclieata. 



Body. The soft-skinned body is long and in 

 appearance strikingly recalls certain Annelida, 

 e.g. Hesione. The body is slightly flattened 

 dorso-ventrally, with arched dorsal side and 



tolerably flat ventral side. The 



integument is 



ft f 



4 



Fio. 289. Peripatus 

 Novae Zealandiaa (after 

 Sedgwick). 



FIG. 290. Peripatus Ectwardsii, Head from the under side. 

 a, Basal portions of the antennae; op, oral papillae. The figure 

 shows also the papillae surrounding the entrance to the oral cavity, 

 and the jaws within the same. 



transversely ringed. The limbs are the only 

 external indications of segmentation. The head 

 is fairly distinct from the trunk. Over the 

 whole body are scattered the wart-like papillae, 

 each of which carries a hollow spine at its point. 

 On each side of the head dorsally there is an eye, 

 and in the middle of the ventral side is the 

 mouth. The anus lies terminally at the posterior end of the body. 



Extremities. The head carries anteriorly and dorsally two ringed 

 and somewhat slender antenna. In the buccal cavity on each side lies 

 a sickle-shaped jaw, consisting of two chitinous plates toothed along 

 their inner sharp edges. On each side of the mouth arises a short 

 ringed process beset with papillae. This process is called the oral or 

 slime papilla. The trunk carries a varying number (14 to 42, accord- 

 ing to the species) of similarly formed limbs. These extremities 

 are placed laterally, at that part where the arched dorsal side bends 

 in to meet the flat ventral side. Each extremity is truncated, 



