] Mr. W. Clark on the Terebrating Mollusca, and on the 



an apparent one, dependent on certain conditions connected with 

 the growth of the animal ; and as the very large anterior gape in 

 all the Pholades is the site of the powerful foot, and is never 

 closed up during their existence, except in this species, I became 

 fully convinced, that the foot, — having finally performed its tere- 

 brating functions, the animal consequently having arrived at full 

 growth (the test of which is the doming and formation of the 

 caliciform incipient tubing, which is in Pholadidea papyracea, 

 the last vestiges of the protecting tubes of the Teredinidce) — had 

 become absorbed, on the well-known principle, that an organ 

 from want of use is often, especially in the lower animals, 

 followed by its total disappearance. This vanishing, depaupe- 

 ration, and withering away of a foot now become useless, and as 

 it were extinct from its complete inclosure, after it had per- 

 formed its appointed duty of excavation, is in strict conformity 

 with Lamarck's views (see page 158, last edition of the ( Ani- 

 maux sans Vertebres '). Thus two most important facts are made 

 evident by this phenomenon, which incontestably proves that the 

 foot, agreeably to Mr. Hancock's views, is the excavator of the 

 animal's dwelling ; and it stamps with additional consideration 

 the Lamarckian doctrine of the progression and advancement of 

 animality resulting from a want requiring to be supplied, which 

 is effected by the concentration of the whole mass of vital energies, 

 the circulation, nervous influences, aided by caloric, the gases, 

 electricity, &c, in forcing and producing the supply of the parti- 

 cular want. That great philosopher instances the addition of 

 tentacula to the Helices in explanation of his views ; and this 

 doctrine is strongly corroborated, if the fact of the obliteration 

 of the foot in Pholadidea papyracea is considered, e contrario, as 

 a retrocession in animalization. This phenomenon also proves 

 that nature never permanently retains what is superfluous, or 

 refuses, as far as its power extends, to supply urgent require- 

 ments. 



This important proof of the soundness of the laws promul- 

 gated by M. Lamarck, that nature mechanically produces the 

 progressive march of animal improvement, almost makes us in- 

 cline to assent to the high and metaphysical researches of that 

 great naturalist, that the doctrine is not without foundation, that 

 the first sparks of vitality arise from gravitation and molecular 

 adherence, aided by the gases put in action by caloric, electri- 

 city, &c. * If we adopt this view, we admit that the germ of vita- 

 lity communicated to matter arises from the mechanical power 

 entrusted to nature ; but we must not for a moment forget that 



* We would respectfully decline following our correspondent in these 

 speculations. — R. T. 



