248 



ZOOLOGY 



The group of mollusks represented by Cldton (Fig. 202, 

 Chiton i- uber) have been referred to the worms by Jlicring, 

 on account of the segmented appearance 

 of the plated shell, and the nervous sys- 

 tem, which 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, ar.d is a trocho- 

 spheie, having a 

 ciliated ring in the 

 F-2 auo.-siug. Nat- 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 



T- ... . ,.,, ,, T , / 7) , IT Fig. 201. End of tentacle 



Littonna httorea, the limpet (Jratella of a snail. , eye; op, optic 

 vulffata), the whelk (Buccinum vn- ncrve; - olfactory ner 



datum], and the Roman snail (Helix 

 ])dt)iatia) are eaten. The sea -ear 

 (Haliotis) is roasted in the shell. 

 The animal of Cymba, Strombus gi- 

 gas, Turbo, Trochus, and Conus are 

 eaten in tlie tropics, wliile many of 

 the larger forms are used 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. 



TIG. 20,5. 



FIG. 203. 



Fie. 202.- Chiton ruber. 

 Y\\i. ~03. Segmented larva 

 of Chiton. 



* In Fissurella and Haliotis the two nerve-cords from the pedal jran- 

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

 \ve have an approach to the double gangliouated cord of worms. 



