252 THE STUDY OF ANIMAL LIFE CHAP. 



South Africa, Tropical America, South America, Tibet, 

 Australia, New Zealand. In the course of ages they have 

 gained very wide representation. Worm-like or cater- 

 pillar-like in appearance, with a soft and beautiful skin, 

 with unjointed legs, with the halves of the ventral nerve - 

 cord far apart, and with many other remarkable features, 

 they are of special interest as " synthetic types " combin- 

 ing certain Annelid characteristics with certain Tracheate 

 or insect characteristics. Thus they resemble Annelids 

 in having nephridia, in the muscular ensheathing of 

 the body, in having cilia in the reproductive ducts, and 

 so on, while they resemble Tracheates in having tracheae 

 (unbranched however), appendages in the service of the 

 mouth, and a long tubular heart. They are shy, noc- 

 turnal, quickly-moving creatures, living a ' ' cryptozoic ' 

 life under leaves and among rotten wood. They snare 

 insects by squirting jets of slime from a pair of papillae 

 beside the mouth. All are viviparous. 



Myriopods. Under this title are included the centi- 

 pedes (Chilopoda), flattened, carnivorous, and poisonous, 



FIG. 73. PERIPATUS. 

 (From Chambers's Encyclop. ; after Moseley.) 



the millipedes (Diplopoda), cylindrical, vegetarian, and 

 harmless, and some more primitive less familiar types. 

 The millipedes have on most of the rings two pairs of 

 appendages and, corresponding to this, two pairs of 

 nerve-centres and breathing openings. It cannot be said 

 that they are nearly related to centipedes, and the 

 resemblance between the two types is one of ' conver- 

 gence," i.e. it is due to similar adaptations to similar 

 conditions of life. Practically, it is important to remem- 

 ber that killing centipedes usually means killing creatures 

 which destroy injurious insects. 

 Insecta. Insects are the birds of the backboneless 



