DIGESTIVE ORGANS. 31 



Mobius has seen Venus mercenarin, and Cypraea Europaen 

 bored tlirongh the shell by Murex orinaeeus, and the soft i)ails 

 eaten.* 



Mr. C. Spence Bate lias proposed the following- theory of the 

 means by vvhieh niollnsks make these perforations. f 



" His observations upon the boring of the Buceinum into the 

 shells of other mollusca attributed their power of perforation to 

 a current of sea-water passing through the l)nceal apparatus, the 

 lingual ribbon having no part in the operation. . The animal 

 takes two days to perforate the shell of Mytilus edulis, and per- 

 forms the work without the least motion of its shell, as must be 

 the case whenever a circular hole is bored by mechanical action. 



The sea-water itself is probably the solvent used in boring by 

 the mollusca, being charged with free carbonic acid ; and is 

 directed bjj- them against the ol)ject to be bored through the 

 process of respiration, and ciliary currents. 



The action of sea-water upon limestone coasts in driving tun- 

 nels and excavating caverns in the rock is evidence of this sol- 

 vent power ; and the same theory will probably account for the 

 absorption of the columella in the Purpuridae as well as other 

 instances of absorption b}^ the animal of portions of its shell." 



1 think that the above theorj^, ingenious as it is, will not ac. 

 count for the perfectly round hole, with clean-cut vertical walls 

 made by boring mollusks in the shells of their prey; indeed it 

 is difficult to imagine any solvent as the unassisted agent in 

 making such a perforation ; yet, on examining a shell not en- 

 tirelj^ bored through, the bottom of the hole is perfectly smooth, 

 showing no marks of mechanical rasping. 



The oesophagus, as already stated, opens into the upper pos- 

 terior end of the mouth. In those mollusks furnished with a 

 proboscis that portion of the a'sophagus which traverses it is 

 much narrowed, and when the proboscis is retracted it is bent 

 into a sigmoid or coil. In its entire length it is provided with 

 interior longitudinal folds. Its middle is dilated into a sort of 

 crop in Voluta, Dolium and some other prosobranchiates. Kefer- 

 stein has found in Triton variegatum, and in Dolium galea that 



* Zool., Oarteyi, 871 1866. 

 ■\ Rept. Brit. Assoc, ll], 1849, 



