. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 704 CONCHIFERA. also occur; these can be aptly enough alluded to in the anatomical description. From what has now been said it is easy to understand the offices performed by the foot. In the lithophagous and xilophagous Con- chifera, the foot, reduced to its rudimen- tary condition, is probably without any par- ticular use, unless perhaps it be among the Pholades, where, being in the form of a sucker, it may enable the animal to fix itself to the parietes of the cavity it inhabits. Among the Conchiferous mollusks that li
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 704 CONCHIFERA. also occur; these can be aptly enough alluded to in the anatomical description. From what has now been said it is easy to understand the offices performed by the foot. In the lithophagous and xilophagous Con- chifera, the foot, reduced to its rudimen- tary condition, is probably without any par- ticular use, unless perhaps it be among the Pholades, where, being in the form of a sucker, it may enable the animal to fix itself to the parietes of the cavity it inhabits. Among the Conchiferous mollusks that live at large, the chief use of the foot is to dig a furrow, into which the animal forces itself partially, and then advances slowly by making slight see- saw or balancing motions, a circumstance which has led Poli to designate the whole class of acephala by the title of Mullusca subidentia. Several of these Mollusks not only make use of the foot in the way we have just mentioned, but also employ it as a means of executing sudden and rapid motions, true leaps, by which they are enabled to change their place with great celerity. It is of course unneces- sary to say that in those genera whose shell is attached immediately to the bodies at the bot- tom of the sea (Chama), the foot is of no use as an organ of locomotion at all events. In the byssiferous species, again, the organ, al- though but slightly developed, is the agent in spinning the filaments of this cable. Nervous system.—Anatomists were long ig- norant of the existence of a nervous system in the Conchiferous mollusca. Poli first disco- vered it in the course of his dissections, whilst preparing subjects for the plates of his magni- ficent work, entitled, Testacea Utriusque Sici- ii(E; but he mistook the nervous system, occa- sionally of considerable magnitude, for one of absorbent or lymphatic vessels, and spoke of it under the name of lacteal vessels. In a very interesting memoir, Mangili exposed the error which Poli
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