THE MOVEMENTS OF SHORE ANIMALS 177 



to return to its " home " is 3 feet. Davis and Fleure 

 (1903), in discussing tlie formation of the scar, state their 

 beUef that it results from the mechanical action of the foot 

 surface, and of the bevelled edge of the shell. During life 

 the animal constantly leaves and returns to its home, and 

 consequentl}*- the foot, in spite of its softness, is responsible 

 for an appreciable amount of wear, especially as fixation is 

 usually preceded by a certain amount of " shuffling or twist- 

 ing round on the scar." The deeper margin of the scar 

 clearly indicates shell action. 



According to Russell (1907) " the seat of the limpet's 

 marvellous sense of direction is quite unknown, and the 

 accuracy with which it returns to a definite spot is very 

 astonishing." From careful experiments with marked 

 limpets this writer concludes : " (i) that every limpet of 

 15 mm. and upwards occupies, for long periods at a time, 

 a definitely fixed position, to which it returns after any 

 wanderings that it may make for food ; (2) that limpets 

 under 15 mm. if not yet settled in a definite position, at 

 least never wander far away, and so generally keep to the 

 same stone ; (3) that limpets wander chiefly when covered 

 by the tide." Results of a similar character have been 

 obtained by other writers for other species of Gasteropod. 

 Pier on (1909), for instance, considers there is evidence of 

 " homing " in Calyptrcea^ but it is less precise than in Patella. 

 Willcox (1905) speaks of the " homing " of Siphonaria 

 alternata and Fissiirella barbadensis, limpets which occur on 

 the calcareous rocks between tide-marks at Bermuda. The 

 former did not " home " if removed more than six inches, 

 but generally returned if moved a couple of inches away, 

 doing best in quiet shallow tide pools. If headed away 

 from the scar Siphonaria turns of its own accord. One 

 specimen formed a new home and made a green spot in 

 three days. The range for Fissurella is about two inches, but 

 otherwise its behaviour is very much like that of Siphonaria. 

 The animals appear to recognise their own scars. 



Before having recourse to explanations involving higher 

 mental activities it is well to consider the part played by 



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