18 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



examination I could never find evidence that the 

 hole was made by the animal, but rather that it 

 had sought lodgment in one of the ready-made 

 cavities. 



Lower down on the tidal belt, where the sand- 

 stone is smooth, being less exposed to the ^veather, 

 the limpets had made little, if any, impression on 

 the rock. 



When we reflect on the growth of the shell, and 

 the habit of the limpet in frequently changing its 

 position, it is difficult to see how the animal could 

 excavate down into the hard rock till the crown of 

 the shell was scarcely seen. Every new extension 

 of the shell would require to open out a new and 

 wider circle of the rock. It is difficult to see how 

 such a pit could be made while the shell continued 

 to grow. True, there is a limit to the growth of 

 the shell ; but does it wait till that limit is reached? 



Dr. Jeffreys states : " Should the rock be soft, it 

 scoops out by degrees ^vith its muscular foot a 

 cavity of greater or less depth." * This is on con- 

 dition that the rock is soft, a condition not required 

 if the limpet can excavate the hard Old Red sand- 

 stone. But without possessing any such poAver, it 

 is in no way surprising that it should make impres- 

 sions on soft rocks, such as chalk, &c., with its 

 strong adhesive foot, carrying more or less of the 

 loose crumbling material in the course of its fre- 

 quent shiftings. 



Reaumur found that the limpet could sustain a 

 weight suspended from the shell of 28 to 30 lbs. for 

 some seconds ; less "weights failed to overcome the 

 resistance. Such viscosity would be a powerful 

 means of carrying away any portion of the rock 

 which had become weak in adhesion. The query 

 may be x)ut : Should the natural habits of the 

 limpet entitle it to be considered a borer, in the 

 true sense of the word, further than in consequence 

 of its strong adhesive foot shifting so frequently off 

 * Brit. Conch., iii. 231. 



