248 



ZOOLOGY 



Fig. 200.— Slug, 

 ural size. 



Nat- 



The group of mollusks represented by Chiton (Fig. 203, 

 Chiton ruber) have been referred to the worms by Jhering, 

 on account of the segmented appearance 

 of the plated shell, and the nervous sys- 

 tem, vi^hich consists of two parallel 

 cords, connected by several commis- 

 sures ; * as well as from the fact that the 

 intestine ends at the hinder end of the 

 body. The young 

 is oval when hatch- 

 ed, and is a trocho- 

 spheie, having a 

 ciliated ring in the 

 middle of the body 

 with a long tuft of 

 large cilia on the head. Afterwards 

 it becomes segmented, as in Fig. 203, 

 and is remarkably worm -like, the 

 limestone plates of the adult corre- 

 sponding to the primitive larval rings. 

 Certain Gastropods are useful either 

 as food or in the arts. In Europe 



7-.,. . ,.,, ,1 T J. /r> J 17 Fig. 201.— End of tentacle 



Littorina httorea, the hmpet {Fatella of a snaii. «, eye ; op, optic 



vulgata), the whelk {Buccinum un- "^""' o, olfactory nerves. 



datum), and the Roman snail {Helix 

 pnmatia) are eaten. The sea -ear 

 {Haliotis) is roasted in the shell. 

 The animal of Cyniba, Stromius gi- 

 gas, Turlo, Trochus, and Conus are 

 eaten in the tropics, while many of 

 the larger forms are use'd for fish- 

 bait. Pearls are sometimes found in 

 the species of Haliotis and Turbo. 

 The beautiful shell of Cassis is made 

 into cameo pins, and the shell of 

 Strombus gigas is in the West Indies made into ornaments. 



* In Fissurella and Haliotis the two nerve-coids from tlie pedal jjan- 

 glia are also united by nine transverse commissures, so that hare also 

 we have an approach to the double gangUonated cord of worms. 



FiQ. 20J. 



I^o. 2C3. 

 Fig. SOU.- Chiton ruber. 

 Fig. 203. —Segmented larva 

 of Chiton. 



