MYRIOPODA. 307 



crystallising out in situ from a mass of yolk, among which is a proto- 

 plasmic reticulum containing nuclei." 



Zoological position. The synthetic characters of Peripattts and 

 its allies may be thus summarised : 



ARTHROPOD AND TRACHEATE 

 ANNELID CHARACTERISTICS. CHARACTERISTICS. 



Segmentally arranged nephridia The presence of trachea. 



' as in Chcetopods. The nature of the heart (a tube 



The muscular ensheathing of the 



body. 

 The cilia in the genital ducts. 



with paired ostia communicat- 

 ing with a pericardium) and 

 the lacunar circulation. 



Less important are the stump-like The modification of appendages 

 hollow legs and the simple as mouth organs, 



eyes. The form of the salivary glands. 



The smallness of the genuine 

 ccelom ; the cavity of the 

 body is hamioccelic. 



The Onychophora differ from other Tracheata Antennata in the 

 simplicity and diffuseness of the trachere, 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, Phyllopod Crustaceans, and Xemerteans) is probably 

 primitive. 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 not certain that the antennce, jaws, and oral papilke of Peripatus 

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

 Insects. 



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

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

 Annelids. 



Second Class of Tracheata Antennata. MYRIOPODA. 

 Centipedes and Millipedes. 



The centipedes and millipedes, which are grouped 

 together in the class Myriopoda, are usually elongated, 

 somewhat vermiform animals, with a distinct head and a 

 very uniform segmented trunk. The head bears eyes 

 (groups of eye spots, not compound eyes like those of 

 insects, except in Scutigera\ jointed antennae, and two or 

 three pairs of jaws. The segments of the trunk bear six- or 

 seven-jointed legs with terminal claws, very similar through- 



