OBSERVATIONS AND CORRESPONDENCE. 



The Limpet's Adhesive Power. 



Having previously ascertained by a series of experiments, made 

 at Folkestone in the summer of 1889, the force necessary to over- 

 come the great powers of adherence of the limpet, I determined 

 to make another series, in order, if possible, to find out the source 

 of these remarkable adhesive properties. 



To do this, I placed several limpets on the side of an empty 

 glass tank ; I then drilled two holes through different rings in the 

 top of each shell, and passed through them a stout copper wire. The 

 ends of this wire were twisted together, and then attached to a spring 

 balance. By pulling on the latter, the force necessary to detach 

 the limpet could be readily observed. Owing to the glass plate it 

 was easily ascertained that no air space existed beneath the foot, 

 which in every part was in close contact with the glass. 



On exercising slight traction on the limpet, the foot and mantle 

 became still more closely applied to the surface of the glass. There 

 was, therefore, nothing to suggest a sucker-like action. 



On injecting the limpet with corrosive sublimate, more than 

 sufficient to immediately destroy all vitality, the shell became quite 

 loose, but still the foot remained adherent. The force necessary to 

 detach the dead limpet was, however, very much less than in the 

 case of the living, for while a force of 35 lbs. was required to 

 remove the living limpet, 25 lbs. sufficed to displace a limpet imme- 

 diately after poisoning. Twenty-four hours after death a force of 

 9^ lbs. detached the limpet. 



When the limpet was dislodged, a thin gelatinous coat remained 

 on the glass wall; this' substance appeared only slightly soluble in 

 sea-water. 



We may, perhaps, be justified in concluding from the above 

 experiments that while some portion of the adhesive power may be 

 due to atmospheric pressure, a very considerable amount, if not the 

 major part, is probably dependent upon the throwing out of a very 

 tenacious substance. In favour of the latter view is the definite 

 evidence of the absence of a vacuum beneath the foot, and the fact 

 that the adhesion continues after the death of the animal, also the 

 positive proof of a tenacious secretion. 



With regard to the secretion of the limpet, it may be mentioned 

 that many species gradually eat their way into the hard strata to 

 Avhich they may be attached — Limestone, Old Red Sandstone, &c. 



J. Lawrence-Hamilton, M.R.C.S. 

 30 Sussex Square, Brighton. 



