DIGESTIVE ORGANS. 99 



little teeth spreading out. The tongue rubs off particles of 

 nourishment onl}^ in the process of retraction, or tears pieces 

 from leaves for example, and draws them into the oral cavity. 

 In seizing and holding the nourishment, the strong annular lip 

 and the jaws are useful accessories. 



As alread}' stated, certain corresponding peculiarities of 

 animals and shells enable us to separate the carnivorous from 

 the ph3'tophagous mollusks ; curiously enough, the arrangement 

 of the lingual ribbon does not always indicate this separation, 

 and we accordinglj- find, in systems of classification based upon 

 this organ, the animal and vegetable feeders rather incongruouslj'- 

 mixed. 



Besides the mastication of food, the teeth are probably used 

 by the carnivorous species in boring through the shells of other 

 mollusks in order to obtain the flesh. It is still a matter of 

 discussion whether this operation is eflfected by mechanical or 

 chemical action or by a combination of both ; but it is generally 

 supposed that the teeth are the tools b}^ which an excavation 

 through the hard shell of the victim is perforated. Most of the 

 large siphonostomate prosobranchiates obtain food in this manner, 

 as well as the Naticas among the holostomates ; and I shall 

 have occasion frequently to refer to the subject hereafter when 

 treating of the individual species. The shells attacked are 

 usually bivalves, which are bored near the beaks where they are 

 thinnest. That instinct is sometimes at fault in these creatures 

 is evidenced by the solid spine of a sea-urchin, which P. P. 

 Carpenter relates, has been bored through by a mollusk. 



On every coast the evidence of this work of destruction is 

 abundant, a large portion of the bivalves washed ashore, being 

 perforated near the umbones. 



Miiller has seen Cerithia on the Brazilian coast bored by 

 Murex Senegalensis, in consequence of which the animal dies 

 and opens its operculum, when a Turbinella comes to share the 

 feast. He has seen a dozen specimens of Cerithium at one time 

 with the Murex extracting the meat through a boring in the 

 spire and the Turbinella at work within the aperture of the 

 shell. When both these are done, a Pagurus crab occupies 

 the empty shell, or shares it with a Crepidula.* 



Mobiusf has seen Venus mercenaria and Cypreea Europaea 

 bored through the shell by Murex ermaceus^ and the soft' parts 

 eaten. 



Mr. C. Spence Bate has proposed the following theory of the 

 means by which mollusks make these perforations. 



" His observations upon the boring of the Buccinum into the 

 shells of other mollusca attributed their power of perforation to 



Jena Zeit, 57, 1871, f Zool. Garten, 371, 1866. 



