328 The Naturalist of Cumbrae. 



The marks which the limpet leaves on [the rock, after 

 browsing on the film of fine seaweed, are themselves 

 interesting. Forbes and Hanley supposed them to 

 be " probably caused by the edge of the shell," but 

 Robertson shows that this cannot be so, for "! find," 

 he says, "that whether the animal is at rest or in 

 motion the shell is a little raised off the surface." 

 Again, in regard to the functions of the tongue, 

 Gwyn Jeffreys states that " this instrument is thrust 

 out from side to side ; and, when charged with food, 

 it is withdrawn into the stomach, unloaded, and 

 again put forth." But Robertson observes, "After 

 long and close watching I never could see it [the 

 limpet] thrust out its long tongue from side to side, 

 and I am strongly impressed that it never does so. 

 That part of the tongue that lies behind the lips, and 

 which is never protruded beyond them, appears to be 

 the only portion applied to the cropping of the 

 filamentous algae while browsing." 



The time and faculties of a man are so limited 

 that even the most cautious philosopher must be 

 content to owe the bulk of his intellectual store to 

 statements which he can never test or prove. Hence 

 it comes to pass that, in natural history, observations 

 upon the habits and characters of different creatures 

 sometimes gain a currency to which they have no sort 

 of valid title. History and romance being thoroughly 

 well intermingled, it is difficult to know where to 

 begin the testing process. Robertson was on the 

 look out for opportunities. He found more than one 

 among his favourite little amphipods. It may be 

 remembered that some time ago Ruskin wrote a note 



