362 



PHYLUM ARTHROPODA 



old-fashioned survivor of an archaic stock. There are about 

 half a dozen genera very luidely distributed. 



The Onychophora'are very beautiful animals. Prof. 

 Sedgwick says : " The exquisite sensitiveness and continu- 

 ally 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." They are shy and nocturnal, 

 with a great dislike to light. They 

 seek out damp places under leaves and 

 among rotting wood. They feed on 

 insects, which they catch by the ejection 

 of slime from the oral papillae. The 

 slime is also squirted out when they 

 are irritated. To their shy habits their 

 persistence is possibly in part due. 

 They are able to move quickly, some- 

 what after the fashion of millipedes, 

 especially like Scolopendrella. They 

 have been seen to climb up vertical 

 glass plates. When at rest or irritated 

 they coil up in a circle. 



Form. — The body suggests an Annelid or a 



caterpillar, but, apart from the appendages, 



there is no external segmentation. There is a 



clear dorso-median line. Over the soft skin are 



numerous minute warts with small bristles. 



The mouth is ventral and anterior ; the anus 



terminal and posterior. 



Appendages.— The first are the large, ringed antenna3 ; then follow 



the sickle-like jaws in the mouth cavity ; a little farther back are two 



oral papillae from which slime is exuded. Then there are the 14-42 



stump-like legs, each with two terminal chitinous claws. 



Skin. — The chitinous cuticle, ordinarily thick in Arthropods, is 

 delicate. It is subject to moulting. The epidermis is a single layer of 

 cells. Beneath it there is a dermis. 



Muscular system. — Externally there is a layer of circular muscles ; 

 within this lies a double layer of diagonal fibres ; internally there are 

 strong longitudinal bundles. Finally, in connection with this internal 

 layer, there are fibres which divide the apparent body cavity into a 

 median and two lateral compartments. The median includes heart, 

 gut, slime glands, reproductive organs ; the laterals include the nerve- 

 cords and salivary glands ; the legs contain nephridia and coxal or 



Fig. 202. — External 

 form of Peripatus. 

 — After Balfour. 



Note antennae and 

 simple legs. 



