J'ound on the Sea-coast near Edinburgh. 1 03 



quired where the operation is constant. In judging of the 

 unseen or unobserved operations of nature, many are guided 

 in their opinion by what appears possible to be effected by the 

 limited powers which a preconceived theory prescribes to the 

 instrument employed. But little is known regarding the time 

 which these instinctive miners take to form their deepening 

 cells. A drop of water falling constantly on the same spot 

 soon leaves evidences of what time, with the smallest force, 

 can effect ; and the keys of musical instruments are, in uo 

 long period, hollowed by the softest touch of the softest fin- 

 gers. There seems no impossibility, therefore, in conceiving 

 that the Pholades may perforate a substance less hard than 

 their own shell by mere attrition, or oven a harder substance, 

 by the constant action of their muscular foot. 



Linnaeus and Lamarck regard the Pholas as a Bivalve shell, 

 with accessory pieces ; while others, from the presence of these 

 auxiliary plates, have classed it among the Multivalves. The 

 animal is hermaphrodite and viviparous, hatching its young 

 in the little sacs of its branchiae. It has a membranous mantle, 

 of a tubular form, open at both extremities, like that of the 

 Solen or Mya. From the superior opening of this tubular 

 mantle two united syphons arise, of which the anterior is the 

 largest. They are slightly dentated on the margin, and serve, 

 the one for the entrance of food, and the other for discharge. 

 When covered by the tide, or in a basin, these tubes may be 

 seen constantly sucking in and ejecting the water. The foot 

 is short and conical, and, from its capacity of being projected 

 and drawn in within its circular covering, probably affixes it- 

 self by suction to the bottom of the hole, and serves as a ful- 

 crum for the rotatory motion of the valves, or even may itself 

 assist in deepening the cell of the animal. Mr Gray, in the 

 third number of the Zoological Journal, has given some ana- 

 tomical details regarding the structure of the Pholades, parti- 

 cularly with regard to the singular falciform projections in 

 the interior of the shell, which he shows are nowise connected 

 with the arrangement of the hinge ; and Poli, in his " superb 

 work" on the Testacea of the Two Sicilies, has given the ana- 

 tomy of the Pholas in detail. The opinion of Poli, it may be 

 added, entirely coincides with the observations I have hazard- 



