356 ARTHROPODS. 



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 morpho- 

 logical importance. It is possible that the mucus 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 antennas, 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. 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 the two classes are branches from 

 one base, and it is likely that the simplest Insects were in 

 some ways like Myriopods. 



Both centipedes and millipedes live on land, but two or 

 three of the latter {e.g., a species of Geofhilus) occur on the 

 sea-shore. Most of them are very shy animals, lurking in 

 dark places and avoiding the light. They breathe like 

 other Tracheata. 



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. The nervous 

 system, heart, excretory tubules, etc., are like those of 

 Insects. 



