10 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 Teredinide)—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 Vertébres’). 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 requirimg 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, &e.* If we adopt this view, we admit that the germ of yita- 
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. 
