252 ARTHROPODS. 



The species acknowledged by Sedgwick are -.—Four from South 

 Africa—/", capensis, P. balfouri, and F. brevis from Table Mountain, 

 and P. mosekyi fiom near Williamstown ; two from Australasia — P. novm 

 zealandice from New Zealand and P. leuckarti from Queensland ; seven 

 from neotropical regions — P. edwardsii from Caracas, P. imthurmi or 

 demeraranus from Demerara, P. triniiiadensis and P. torquaius from 

 Trinidad, P. iuliformis from St. Vincent, P. chilensis from Chili, P. 

 quitensis from Ecuador, besides which there are some doubtful forms. 

 I have quoted the species in order to illustrate how widely this remark- 

 able genus is distributed. 



As the different species have similar habits and live in 

 very similar conditions, the differences between them per- 

 haps illustrate purely constitutional variations. 



A more Detailed Account of Peripatus. 



Form — The body suggests an Annelid or a caterpillar, hut apart from 

 the appendages there is no external segmentation. Over the soft skin 

 are numerous minute warts with small bristles. The mouth is ventral 

 anteriorly ; the anus is terminal posteriorly. 



Appendages. — The two large, ringed antennae 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 papilliE 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. 



The Muscular System is very well developed. ( I ) 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 contain 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 Nervous 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. They are not 

 ganglionatcd, but are covered by 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, etc., and two viscerals or 

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



