PULMONAEY GASTEROPODS. 411 



covered and uncovered by the waves. They are almost always 

 attached to rocks, or other submerged bodies, to which they adhere 

 with great tenacity. If the common Limpet (Patella vulgata) is 

 alarmed before any attempt is made to dislodge it, no human force, 

 pulling in a direct line, can remove it, and it can sustain without 

 being crushed a weight of many pounds. It holds on by the great 

 quantity of vertical fibres of the foot, which in raising the median 

 part forms in the centre a sort of sucker. It is the celebrated experi- 

 ment, of the Magdeburg cups which these little molluscs realise by 

 their vital action. 



These animals bury themselves in the chalky rocks to the depth 

 of two or three lines ; when they are dispersed, they are observed 

 constantly to return to the same place. Their movements are, besides, 

 extremely slow; the advance of the Limpet being only perceived 

 by watching the slow upheaval of the shell above the plane of its 

 position. It is supposed, from the mouth being armed on its upper 

 edge with a large semi-lunar, horny, cutting tooth, and in its lower 

 part from having a tongue furnished with horny hooks, and from 

 their inhabiting in great numbers places covered with marine plants, 

 that their food is chiefly vegetable. 



Fig. 212. Patella caeruleu (Lamarck). Fig. 213. Patella umbella (Gmel.). 



The poorer inhabitants of the coast eat limpets when they have 

 nothing else, but their flesh is singularly coriaceous and indigestible. 



They are found in every sea; but are, however, found to be 

 larger as well as more numerous, and much richer in colour, in 

 Equatorial seas, and especially in the southern hemisphere, than in 

 European seas. They attain, in fact, their maximum of development 

 here ; for in the Straits of Magellan species are found as large as a 

 slop-basin, which the natives use for culinary purposes. 



The common Limpet is thick, solid, oval, and nearly circular, 



