208 



ZOOLOGY 



The group of mollusks represented by Chiton (Fig. 207, 

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

 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, and is a trocho- 

 spheie, having a 

 ciliated ring in the 

 Fig. 205.-siug. Nat- middle of the body 

 with a long tuft of 



large cilia on the head. Afterwards 

 it becomes segmented, as in Fig. 208, 

 and is remarkably worm -like, the 

 limestone plates of the adult corre- 

 sponding to the primitive larval rings. 

 Certain Gastropods are usefiil either 

 as food or in the arts. In Europe 



T ... . ,.,, ,-, ,. Lt-n j.ii Fi S- 206. End of tentacle 



Littonna littorea, the limpet (Patella O f a snail, e, eye ; op, optic 



vulgata), the whelk (Buccinum un- : 



datum), and the Roman snail (Helix 

 pomatia) 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 the tropics, while 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. 



* In FissureUa 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. 



FIG. 207. 



FIG. 208. 



Fjg. 207 Chiton ruber. 

 Fig. 208. Segmented larva 



