THE BEHAVIOR OF LIMPETS 389 



3. The clinging of the limpets. — Limpets are completely help- 

 less when removed from the rocks. If dropped into still water, 

 they invariably fall with the shell side down and unless righted 

 by some external force will remain in this position, perfectly 

 helpless, until dead. Individuals dropped into an aquarium 

 at first made attempts to right themselves by stretching the 

 foot up out of the shell. They were unable to turn over, how- 

 ever, and after 48 hours, all were dead. 



This helplessness when detached, suggests that the marked 

 ability to survive and multiply, which limpets possess, must 

 be accompanied by an ability to prevent themselves ever being 

 detached. To ascertain with what force they cling to the rocks, 

 a pair of miniature, three-clawed tongs was made from large 

 fish hooks, and employed in pulling the animals from their 

 attachments. The sharpened points of the claws of the tongs 

 were hammered into knife edges so that they could be easily 

 inserted under the edges of the limpets' shells. With the limpet 

 attached to the rock the tongs were adjusted in such a manner, 

 that the animal could be lifted directly from its resting place 

 by a pull, perpendicular to the rock's surface. A spring balance, 

 that had previously been calibrated, was hooked into the 

 eye ends of the tongs and a steady pull detached the limpet 

 from the rock. By noting the figure reached by the indicator 

 of the scale just as the limpet left the rock, the pull necessary 

 to overcome the attachment of the limpet's foot was determined. 



Limpets of various sizes and species were tested with the 

 following results. No marked specific differences in clinging 

 power were observed, the recorded differences being directly 

 correlated with the area of the foot of the individual. 



The figures show a variation from 5 lbs., the force required 

 to detach the smallest limpet tested, to 48 lbs. for the largest. 

 The foot of the smallest animal was 2.2 cm. long and 1.8 cm. 

 wide, while that of the largest was 4.3 cm. by 3.2 cm. 



It was noted that the limpets need not be attached to a 

 smooth surface, but rather the contrary, if they are to display 

 their best clinging ability. Limpets that were attached to 

 barnacle covered rocks seemed to cling with fully as much force 

 as those attached to the fairly smooth, but wave eroded, rock 

 surface. When limpets were pulled from barnacle encrusted 

 rocks, the barnacles with which the foot of the animal was 



