PHOLAS. 181 
claim particular notice, as much error has existed with respect 
to them: their utility originates from the two very strong 
muscular bands given off from the foot, which are fixed to 
their spatulate roughened terminations, and serve as points 
@appui for its action in the work of excavation, without en- 
dangering or distressing the body. We have here a beautiful 
illustration of the resources of nature to accomplish what is 
necessary for the well-bemg of her creations; for if the foot 
was attached to the body as in the ordinary bivalves, without 
aid, the severe action of excavation would probably paralyse 
the animal and tear it from its natural position, which result 
is prevented by this admirable contrivance, and the body lies 
securely supported in the curvature of these appendages, 
whilst the movement of the foot is altogether maimtained by 
working from the crotchets. 
Nature has not given this animal an anterior adductor, 
because it is unnecessary, as it rarely expands the large 
gape by a separation of the valves; and when it does, the 
medial adductor and the limited action of the ligament suf- 
fice: the permanent gape is the equivalent for what in ordi- 
nary bivalves is effected by the opening and closing of the 
shell by the adductor muscles. The apophysary and pedal 
apparatus are not the substitutes for an anterior adductor 
muscle ; for if they did act as such, their muscular powers 
must remain in quetude from the necessary contraction, and 
the excavating action would be destroyed: the two actions 
are completely antagonistic. The posterior part of the valves 
is only opened shghtly to allow the issue of the basal portion 
of the branchial sheath, to assist by attrition in the enlarge- 
ment of the posterior part of the chamber whilst the foot is 
operating im front. 
The foot and pedicle, which in a living state appear almost 
hyaline, when they have become exsiccated, will be found to 
consist of a mass of longitudinal elastic fibres, the principal 
portion of which centre on the umbonal excrescences, and the 
remainder supply muscular threads to the anterior part of the 
body: the basal area of the foot is by far the most coriaceous 
portion. 
