Boclc-Borers, 109 



tliese Eock -borers work tlieir way into and tlirougli 

 liard stones. Some naturalists assert tliat tliey 

 effect this by means of an acid wbicb. decomposes 

 the substance of tlie rock, and renders it soft ; 

 others^ tliat tlie animal keeps turning round and 

 round like an instrument called an auger^ and so 

 gradually rasps away tlie surface of tlie stone with 

 the angles of its sliell_, but we question wlietker 

 the shell would not be worn out first in such a pro- 

 cess. The generic name of these '^ stone-piercers/^ 

 comes from the Greek word Fholeo — to hide, and 

 the rocky chambers which they hollow out for them- 

 selveSj are as snug hiding-places as can well be 

 imagined; yet however deep they may go into 

 these gloomy caverns^ as we should be apt to 

 suppose them, they need not be in darkness ; for it 

 appears that these Pholades emit a most remarkable 

 light — whether phosphorescent or not does not 

 appear to be determined ; so strong is it_, that it is 

 said to illuminate the mouth of the person who eats 

 the molluskj and it is remarked by Dr. Priestly, 

 that ^^ contrary to the nature of most fish, which 

 give light when they tend to putrescence, this is 

 more luminous the fresher it is, and when dried its 

 light will revive on being moistened with water.^"* 

 So that in more respects than one these Eock-borers 



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