MYRIOPODA. 



291 



ANNELID CHARACTERISTICS. TRACHEATE CHARACTERISTICS. 



The presence of tracheae. 



The nature of the heart and the 



lacunar circulation. 

 The modification of appendages 



as mouth organs. 

 The form of the salivary glands. 

 The smallness of the genuine 



body cavity or ccelome. 



Segmentally arranged nephridia as 

 in Chaetopods. 



Segmentally arranged coxal glands, 

 like similar glands in some 

 Chaetopods. 



The muscular ensheathing of the 

 body. 



Less important are the stump- 

 like legs and the simple 

 eyes. 



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

 Molluscs, Phyllopod Crustaceans, and Nemerteans) 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 coxal or crural glands, and that the latter are 

 homologous with the parapodial glands of some Annelids. It is not 

 certain that the antennae, jaws, and oral papillae of Peripatus precisely 

 correspond to the antennae, mandibles, and first maxillae of Insects. 



Our general conclusion is that Peripatus is an archaic type, a survivor 

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

 Annelids. 



Second Class of Tracheata Antennata. MYRIOPODA. 

 Centipedes and Millipedes. 



These animals retain a worm-like shape ; the numerous 

 rings of the body and the appendages they bear are very 

 uniform ; there is little division of labour. It would be rash 

 to assert that any of the modern Myriopods are stages in the 

 pedigree of Insects, but it is likely that the two classes are 

 branches from one base. Simple wingless insects, known 

 as Collembola and Thysanura, are closely approached by 

 such Myriopods as Scolopendrella. 



Both centipedes and millipedes live on land, but two or 

 three of the latter (e.g., a species of Geophilus) occur on the 

 seashore. Most are very shy animals, lurking in dark places 

 and avoiding the light. 



The head bears a pair of antennae, and two pairs of 

 appendages mandibles and maxillae. The limbs are six- 

 or seven-jointed, clawed, and very uniform. They have 

 many more legs than insects, but they make less of them. 

 The nervous system, heart, excretory tubules, &c., are like 

 those of Insects. 



