CONCHIFERA. 43 



The notion that Oysters can be fattened on oat- 

 meal is a vulgar eiTor. 



The stomach and intestine are very simple, and 

 the latter opens into the chamber of the dis- 

 charging siphon. 



The nervous system now becomes well de- 

 veloped. It consists of three pairs of principal 

 ganglions with their branches. 



Organs of sense are likewise possessed by this 

 Class in an advanced condition of development. 

 Besides the palps just noticed, many of the spe- 

 cies which have the mantle open carry sensitive 

 lengthened tentacles along its borders, set some- 

 times in a single, sometimes in double rows. In 

 the Scallops (Pecteii), these are seen to great ad- 

 vantage. The openings of the siphons are also 

 generally protected by tentacles, which close down 

 and form a sort of network across the orifice. In 

 Pholas dactylus, these are cmiously branched, like 

 the tentacles which surround the mouth of the 

 HolothurmJ^ 



The organs of hearing consist of a pair of trans- 

 parent capsules filled with a clear fluid. Each 

 contains a glassy globule, which constantly main- 

 tains a very singular swinging and rotatory motion, 

 that instantly ceases when the capsule is ruptui'ed. 

 These capsules are situated in the foot. 



Organs of vision are much more obvious, at 

 least in many species, being often highly coloured, 



" The important part which this apparatus serves in the taking 

 of food, may be seen by covering the palps of Anodonta, &c., 

 with any coloured powder. This powder is carried by the cilia 

 from the surface to the borders of the palps, thence upon their 

 transversely grooved internal surfaces into the angle fonned by 

 these latter, thence into currents of the grooves, and so direct 

 into the mouth." — Siebold's Anat. of the Invertehrata, § 189. 

 * See my "Devonshire Coast," p. QQ, and pi. ii. 



