io GENERAL SURVEY OF THE ANIMAL KINGDOM. 



Myriopods, Insects, Spiders, and other forms, which have 



segmented bilaterally symmetrical 

 bodies and jointed appendages. 

 The skin produces an external 

 cuticle, the organic part of which 

 consists of a substance called chitin, 

 associated in Crustaceans with 

 carbonate of lime. The nervous 

 system consists of a dorsal brain, 

 connected, by a nerve-ring around 

 the gullet, with a ventral chain 

 of ganglia. 



Echinoderms.- -This is a well- 

 defined series, including star-fishes, 



brittle-stars, sea-urchins, sea-cucumbers, and feather-stars. 

 The symmetry of the adult is usually radial, though that 

 of the larva is bilateral. A peculiar system, known as the 

 water-vascular system, is characteristic, and is turned to 

 various uses, as in 

 locomotion and respira- 

 tion. There is a 

 marked tendency to 

 deposition of lime in 

 the tissues. The de- 

 velopment is strangely 



FlG. 12. Spider. 



or 



in- 



" worm ' 



For 



circuitous 

 direct." 



Segmented "worms." 

 -It is hopeless at 

 present to arrange 

 with any definiteness 

 those heterogeneous 

 forms to which the title 

 is given, 

 this title is little 

 more than a name for 



a shape, assumed by animals of varied nature who began 

 to move head foremost and to acquire sides. There is 

 no class of "worms," but an assemblage a mob not 

 yet reduced to order. It seems useful, however, to separate 

 those which are ringed or segmented, from those which 



FIG. 13. Crinoid or feather-star. 



