248 



ZOOLOGY 



F g. 200.— Slug, 

 ural f ize. 



Nat- 



Tlie group of molliisks represented by Cliifon (Tig. 202, 

 CUton ruber) have been referred to the vroTms by Jhering, 

 on account of the segmented appeaiauee 

 of the plated shell, and the nerrous sys- 

 tem, vhich consists of tivo 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 OTal when hatch- 

 ed, ard 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. 503, 

 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 

 Littorina littorea, the limpet {Patella of a^'snau! 

 vulgata), the whelk {Buccinum iin- 



datum), and tlie Roman snail {Helix 

 jjimiatiq) are eaten. Tlie sea - ear 

 {Raliotis) is roasted in the shell. 

 The animal of Ct/mba, Sfrombus gi- 

 gas, Tiirbo, Troclius, and Cvmis are 

 eaten in the tropics, while many of 

 the larger forms are used for fish- 

 bait. Pearls are sometimes found in 

 the species of Haliofis and Turbo. 

 The beautiful shell of Cassis is made 

 into cameo pins, and the shell of 

 Sfrombus gigas is in the West Indies made into ornaments. 



* In Piisurella and Haliotis the two nerve-cords from the pedal gan- 

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

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



End uf tentacle 

 e, eye ; op, optic 

 nerve ; o, olfactory nerves. 



Fig. 20: 



Fig. 203. 

 Fi?. 202— CAiton ruber. 

 Fii; 203. — Segmented larva 

 of CkUuii. 



