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 

 d'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-being 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 maintained 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 quietude 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 slightly to allow the issue of tbe 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 in 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. 



