198 THE FOOD OF ANIMALS 



down and listening attentively a curious rasping sound will be 

 heard, and a little care will show that this is produced by the 

 limpets, some of which will be found to have left their homes, 

 crawling slowly about in the search for food. Selecting one of 

 these, and watching it closely, we shall soon find that the rasping 

 noise is caused by the tooth-studded radula, which is protruded 

 from the mouth and brought to bear with steady strokes upon 

 the crust of algae, cleaning this off as effectively as could be done 

 by means of a strip of sand-paper. Meanwhile the limpet crawls 

 slowly onwards, moving its snout from side to side, and now and 

 then touching the rock with its mobile pointed feelers. Fre- 

 quently an individual may be seen to rear itself up against a 

 neighbour's shell, and engage in a bit of friendly house-cleaning. 

 Examination of the neighbourhood of a deeply-sunk scar, which 

 has been occupied for a long time, clearly reveals the large amount 

 of scraping that has been done. As the adjoining supply gets 

 low the limpet wanders farther and farther from home, and is 

 sometimes found as far as 9 feet from its scar. It is clear that 

 such a method of feeding must quickly wear away the rasping 

 ribbon, but this rapidly grows forward, like a finger-nail (see 

 p. 95), as it is used up, the reserve part of it being situated in a 

 long sheath at the back of the thick-walled pharynx within which 

 the mouth-cavity is placed. It is particularly interesting to note 

 that the reserve portion is of extraordinary length in this case, 

 a fact which may perhaps be correlated with unusually rapid 

 wear. 



The Limpet's feeding possibilities have not, however, been 

 exhausted in the preceding description. Many individuals live 

 in the , neighbourhood of the large brown sea- weeds (species of 

 Fucus and Ozothallia) known as " wrack ", which are common on 

 our coasts. These furnish food to a number of sea-snails, the 

 Limpet being one of them. The present writer was on one 

 occasion fortunate enough to find a limpet actually at work 

 upon the edge of a piece of wrack. This was firmly embraced 

 by the flexible lip, which entirely surrounds the mouth-opening, 

 and held firmly by the strong upper jaw. The radula was then 

 brought to bear from below, and by its rasping action a curved 

 piece of sea- weed was soon scraped away, the injured part 

 suggesting the appearance of a piece of bread-and-butter after 

 some school-boy has taken a bite. 



