HABITS OF THE PHOLAS. 245 



It must be evident, then, that neither the likeness 

 of the animal, nor the formation of its singular 

 dwelling-place, can be seen by the casual wanderer 

 along the sea-shore. 



It will also be apparent to the intelligent reader, 

 that when once the Pholas is located in a certain 

 spot, he becomes a tenant for life ; for never by any 

 chance whatever, can the poor miner leave his rocky 

 habitation by his own unaided exertions, even were 

 he so inclined. As he grows older and increases in 

 size, nature teaches the animal to enlarge his habita- 

 tion in a proportionate and suitable manner. 



During the period of the boring process, the ori- 

 fice becomes clogged above the shell with the debris 

 of the rock, and this, if allowed to accumulate would 

 speedily asphyxiate the animal. To get rid of such 

 an unpleasant obstruction, the Pholas retracts, and 

 closes the end of its siphons, then suddenly extends 

 the ' double barrelled ' tube to its full length, until it 

 reaches the entrance of the tunnel. This movement 

 often repeated, causes portions of the pulverized stone 

 to be forced outwards at each operation. 



It is interesting to watch the curious manner in 

 which the end of the principal siphon is alternately 

 closed and spread out when it reaches the water, 

 like a man inspiring heavily after any unusual exer- 

 tion ; it is then made again to descend, and renew 

 its task, as above described. 



In extracting that portion of the debris which is 



