PATELLA. 233 



ance. He attributed the adhesive force not to muscular 

 action^ but to an invisible glue which exudes from the 

 granulated base or sole of the foot. It may be also 

 caused by an" adaptation of the surface of this part of 

 the animal to the frequent^ although often minute, 

 inequalities of the stone; although the glutinous and 

 viscous fluid, which is secreted by numerous glands in 

 the foot, appears to be the principal agent. It is said 

 that death does not destroy the cohesion ; but I do not 

 see how such an experiment could be tried. Dr. John- 

 ston, in his ' Introduction to Conchology,^ likewise states 

 that if, after having detached a Patella, one^s finger be 

 applied to the foot of the animal, or to the spot on which 

 it rested, the finger will be held there by a very sensible 

 attraction ; and that if the spot be then moistened with 

 a little water, no further adhesion will occur, the glue 

 having become dissolved or weakened. When the 

 limpet wishes to leave its abode, it has only to raise 

 gently the edges of the foot to admit the sea and loosen 

 the cement. Adanson believed that the adhesion was 

 owing to the action of numerous hemispherical suckers 

 on the under surface of the foot, aided by a viscous 

 secretion ; he observed that when the animal was de- 

 tached fr^om the rock, those suckers expanded or assumed 

 a globular form. The foot is undoubtedly capable of 

 considerable dilatation and contraction, and has a vas- 

 cular structure ; it is often much distended with water. 

 This great French naturalist does not seem to have 

 known the branchial organization of Patella-, for he 

 describes the gills as an appendage of the mantle. It 

 was supposed by Cuvier that the common limpet was 

 hermaphrodite. Adanson and Milne-Edwards, however, 

 established the fact of its bisexuality ; and Lebert and 

 Robin published in the *^Annales des Sciences Naturclles ^ 



