STATIONARY GASTEROPODS. 147 



from many familiar trials of its strength, how firmly the 

 animal doth adhere. Reaumur ascertained that a weight of 

 twenty-eight or thirty pounds was required to overcome the 

 force of it. This astonishing power in so small and hebet- 

 ous an animal does not depend on the muscularity of the 

 foot, nor on any mechanical engraining of its surface with 

 the pores of the stone, nor on any vacuum produced under 

 it ; for Reaumur disproved all these explanations by some 

 decisive experiments. He cut the animal from top to 

 bottom in two halves as it stood fixed perpendicularly on 

 the rock, and he made other deep incisions in a horizontal 

 direction, destroying in this manner all the muscular power 

 of its base, and all supposable vacuity between it and the 

 stone, but the adhesion continued as firm as before the 

 experiment. Even the death of the limpet does not destroy 

 the cohesion. This entirely depends on a glue, or kind of 

 paste, which, although invisible, produces a very consi- 

 derable effect. If, after having detached a Patella, the 

 finger is 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 resistance, although no glue is perceptible. And it 

 is remarkable, that if the spot is now moistened with a little 

 water, or if the base of the animal is cut, and the water 

 contained in it allowed to flow over the spot, no further 

 adhesion will occur on the application of the finger, the 

 glue has been dissolved. It is Nature's solvent by which 

 the animal loosens its own connection to the rock. When 

 the storm rages, or when an enemy is abroad, it glues itself 

 firmly to its rest ; but when the danger has passed, to free 

 itself from this enforced constraint, a little water is pressed 

 from the foot, the cement is weakened and dissolved, and it 

 is at liberty to raise itself and be at large. The fluid of 

 cementation, as well as the watery solvent, are secreted in 

 an infinity of miliary glands, with which the foot is, as it 

 were, shagreened;* and as the limpet cannot supply the 

 secretion as fast as this can be exhausted, you may destroy 

 the animal's capacity of fixation by detaching it forcibly two 

 or three times in succession. 



Of the habits of the Patella, so far as they concern us 

 at present, Mr. Lukis, of Guernsey, gives the following 

 account : " The locomotion of the limpet may be ascer- 



* Adanson took these glands for little suckers, to whose combined action 

 he attributed principally the animal's adhesion. Seneg. p. 31. 



In the Onchidium peronii, in some species of Doris, and particularly in 

 the Onchidore, the foot is sprinkled over with a great number of vesicles or 

 vesicular tubercles. BLAINVILLE in Journ. de Physique, Ixxxv, p. 439. 



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