NOTES OX THE COINKVION LIMPET. 17 



by the edge of the shell."* I find that whether the 

 animal is at rest or in motion the shell is a little 

 raised off the surface, which explains why it is so 

 easily driven off the rock by the first blo^v; and if 

 success does not attend the first attempt, it is 

 difficult afterwards to succeed without damaging 

 the shell. If the shell is tapped uj)on before being 

 disturbed, it is seen to jerk down on the rock, 

 closing up the intervening space. From this we 

 may infer that it is more likely that the fucoid-like 

 tracks Avere caused by the teeth of the animal 

 cropping the algae than by the edge of the shell. 



The elevation of the shell from the rock allows at 

 all times a free flow of aerified water to the limpet, 

 and affords a possible means of food getting in to 

 it while confined to a particular spot. 



When the animal is laid ojien the tongue is seen 

 to stretch down and fold into a few irregular con- 

 volutions on the right side, and then double back on 

 itself till near the head. When stretched out it .is 

 about double the length of the shell, but varies 

 more or less in different individuals. 



In regard to the boring or excavating powers of 

 the limpet, Dr. Jeffreys says : " Mr. Anderson of 

 Wick (the highly intelligent editor of the 'John O' 

 Groat Journal '), gave me some jDieces of Old Red 

 sandstone from that coast, in which the pits made 

 and inhabited by P. nil gat a were so deep, that 

 little more than the crown of the shell was visible 

 outside." t In this case I suspect that there has 

 been some mistake. All round the coast of the 

 Firth of Clyde where sandstone has been weathered 

 into cup-shaped cavities of various sizes these are 

 numerously inhabited by the limpet. Among hun- 

 dreds of these animals found in such cavities, it is 

 not difficult to find some whose shells fit the 

 cavities very exactly. I have searched over con- 

 siderable tracts of the shore, and often found 

 limpets closely fitted into such holes; but on closer 

 * Brit. MoU., ii. 425. f Brit Cwich., iii. 231. 



