82 THE SEA-SIDE AND AQUAEIUM. 



delicate, fleshy foot, entirely protruding through the 

 rock, as I have represented in the Frontispiece. 



During the period in which the Pholas was actually 

 engaged in boring, it continually threw out from its 

 smallest (anal) syphon fine threads of apparently pul- 

 verised rock. These produced a very strange effect. 

 Had my favourite been totally imbedded, I should 

 naturally have supposed, as Mr Osier does, that in 

 order to free itself from the soft particles that occlude 

 its orifice, it would contract its syphon, then sud- 

 denly extend it, at same time blowing away the 

 debris, and thus clearing the cavity. But such could 

 not possibly be the case in this specimen, for the 

 rock was shaped so that, as I have before stated, the 

 whole of the syphons, and part of the valves, were 

 always exposed, and never at any time entirely 

 covered, even with the softened particles produced by 

 the boring operation. 



This phenomenon, therefore, evidently admits of 

 no other explanation, than that there must be some 

 pedal opening through which the creature draws in 

 whatever collects at the base of the cavity, and expels 

 it as above mentioned, and this without any filtra- 

 tion whatever. 



I candidly confess that I have never been able to 

 discover any pedal orifice ; but upon no other supposi- 

 tion can I apprehend how it is that these threads 

 lie about by hundreds in all directions, the animal 

 ejecting them at least once in every quarter of an 

 hour during the time it is at work; yet, when in a 



