DETAILED ACCOUNT OF PERIPATUS. 287 



Appendages. — The two large, ringed antennee do not seem to be 

 homologous with limbs. The first pair of appendages — double sickle- 

 like jaws — lie in the mouth cavity. A little further 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. In the young P. 

 capensis the leg is said to be five-jointed, but in the adults there is no 

 trace of this. In respect to its legs, therefore, Peripatus is hardly an 

 Arthropod. 



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

 delicate. The ectoderm [hypodermis, or epidermis] is a single layer of 

 cells. 



T\\t Muscular System is very well developed. (l) Externally there 

 is a layer of circular muscles ; (2) within this lies a double layer of 

 diagonal fibres ; (3) internally there are strong longitudinal bundles. 

 Finally, in connection with this internal layer, there are fibres which 

 divide the body cavity into a median and two lateral compartments. 

 The median includes heart, gut, slime glands, reproductive organs ; 

 the laterals include the nerve cords, the salivary glands ; the legs con- 

 tain nephridia and coxal or crural glands. Striped, rapidly contracting 

 muscles are characteristic of Arthropods, but in Peripatus the muscles 

 are unstriped, excepting those which work the jaws and are perhaps the 

 most active. 



The Nerzwus System consists of a dorsal brain and two widely separate 

 lateral ventral nerve cords. These are connected transversely by numer- 

 ous commissures, are slightly swollen opposite each pair of legs to which 

 they give off nerves, and are united posteriorly over the anus. There 

 are only hints of gangba, but there is a continuous layer of ganglionic 

 cells. The brain is very homogeneous, simpler than that of most Insects. 

 From the brain nerves pass to the antennje, &c., and two viscerals or 

 sympathetics, soon uniting, innervate the anterior part of the gut. 

 Sense organs are represented by two simple eyes on the top of the head. 

 These are most like the eyes of some marine Annelids. Behind each 

 there lies a special optic lobe connected with the brain, but the eye itself 

 arises as a dimple in the skin. 



Alimentary Canal. — Round about the mouth, papilla; seem to have 

 fused to form a " mouth cavity," which includes the mandibles, a median 

 pad or tongue, and the opening of the mouth proper. The mouth leads 

 into a muscular pharynx, into which opens the common duct of two 

 large salivary glands, which extend far back along the body. Mouth, 

 pharynx, and short cesophagus are lined by a chitinous cuticle, like that 

 of the exterior. The long digestive region or mid gut extends from the 

 second leg nearly to the end of the body. Its walls are plaited. Finally, 

 there is a short rectum, lined by a chitinous cuticle. 



Circulatory System. — The dorsal blood vessel forms a long contractile 

 heart. It lies within a pericardial space, and receives blood by seg- 

 mentally arranged apertures with valves. The circulation is mostly in 

 ill-defined spaces in the apparent body cavity or "hKmoccele." 



The Respiratory System consists of very long and very fine unbranched 

 tracheae, which are widely distributed in the body ; a number open 

 together to the exterior in flask-like depressions. These openings or 

 stigmata are diffuse and irregular in Peripatus edwardsii. but in P, capensis 



