366 



PHYLUM ARTHROPODA 



The Onychophora differ from other Tracheata Antennata in the 

 simphcity and diffuseness of the tracheae, in having only one pair of 

 jaws, in the absence of external segmentation, in the nature of the 

 body wall, and so forth. 



The ladder-like character of the ventral nervous system (cf. primitive 

 Molluscs, Ph^^llopod Crustaceans, and Nemerteans) is probably primi- 

 tive. That salivary glands and genital ducts are homologous with 

 nephridia is a fact of much morphological interest. It is possible that 

 the slime glands are modifications of crural glands, and that the latter 

 are homologous with the parapodial glands of some Annelids. It is 



Fig. 205. — A millipede. 



Fig. 206. — A centipede. 



not certain that the antennae, jaws, and oral papillae of Peripatus 

 precisely correspond to the antennae, mandibles, and first maxillae of 

 Insects. 



Qur general conclusion is that Peripatus is an archaic type, a sur- 

 vivor of forms which were ancestral to Tracheata and closely related to 

 Annelids. 



Like some other archaic types, e.g. Dipnoi, the Onychophora have a 

 very wide range of distribution, which may be briefly indicated : — 

 Peripatus (tropical America and tropical Africa) ; Eoperipatus (Indo- 

 Malay) ; Peripatoides and Ooperipatus (Australasia) ; Opisthopaius 

 (Chili and South Africa) ; Paraperipatus (New Britain) ; Peripatopsis 

 (Central Africa). 



