488 THE AQUARIAN NATURALIST. 



diffused through the water wherein the creatures are 

 confined. It will then be seen that powerful currents 

 are perpetually rushing through the extremities of 

 each siphon, caused by the rapid action of cilia placed 

 within ; and that the streams thus produced not only 

 form a provision for constantly changing the water in 

 which the branchiae are immersed, but forcibly convey 

 floating molecules to the aperture of the mouth, 

 which occupies a position very similar to that of the 

 Scallop, described in a preceding page, and thus 

 supplies abundance of nutritive materials, that could, 

 in animals so destitute of prehensile organs, have 

 been procured by no other contrivance. The whole 

 arrangement, indeed, very closely resembles what we 

 have already witnessed in the Ascidian races ; only, 

 instead of being merely agglutinated to foreign sub- 

 stances, the Pholades excavate for themselves a sub- 

 terranean residence, wherein, living a life of comfort- 

 able indolence, they pass their time, and 



. ..." in their pearly shells, at ease attend 

 Moist nutriment." 



The abodes of the Pholas dactylus are generally in 

 black, sandy mud, and their colonies are readily 

 discovered by treading heavily, or striking the beach 

 with a stick, whereupon the alarmed inmates spirt 

 water from their burrows; and on digging at the 

 places thus indicated, the animals are easily exposed, 

 each holding firmly to the interior of its den by 

 means of its great foot, which cannot be withdrawn 

 into the shell, and resembles a piece of translucent ice. 



Placed in a vessel of sea- water, the smaller speci- 



