362 Natural Historic of Molluscous Animals, 



undatum), so common on our coasts, and of which Mr. Osier 

 gives the following interesting account. " As in the bivalves 

 inhabiting sand, its foot is the instrument of penetration ; and, 

 like them, it has the power of distending this organ to a size 

 nearly, if not quite, equal to that of the shell, A section of 

 the foot shows it to be divided into two nearly equal parts ; 

 the powerful muscle which extends from the operculum to 

 the spire forming the upper or posterior half, and a cellular 

 spongy mass constituting the remainder. The lower surface 

 of this portion is the disc on which the animal crawls ; and, 

 being considerably longer than the muscle, it is folded upon 

 itself, when retracted within the shell; and the operculum 

 lies flat above it, when it is projected and extended. A trans- 

 verse section of the foot, near the part where it joins the 

 body, shows four considerable tubes penetrating the spongy 

 portion, and very near each other ; three of which are in a 

 line parallel to, and almost in contact with, the muscle ; the 

 fourth a little below the middle one of the three. By a 

 series of transverse sections of the foot, parallel to the oper- 

 culum, we are enabled to trace these tubes ; and to ascertain 

 that they become rapidly smaller as they advance, until they 

 are quite lost ; the longest of them not admitting of being 

 traced quite to the operculum. All these tubes are given off 

 at the extreme anterior point of the thorax from a consider- 

 able one {J^g, 65, /),* which, being situated under the muscular 



floor of this cavity, 



^ ' takes a direction 



/ to the right side, 



h . / It terminates near- 



^ ,• ly midway be- 



tween the heart 



* « The animal of ^uccinum undatum ; part of the spire of the bran- 

 chiae removed; the mantle turned to the right side; the upper part of the 

 thorax cut away to expose its cavity, from which the boring trunk and 

 salivary glands have been taken, a a, The foot; b, the head ; c, a kind of 

 platform raised above the floor of the thoracic cavity, on which the point 

 of the boring trunk rests, and which leads to the mouth ; dy the cavity of 

 the thorax; e, the mantle; /, the rectum; g, the stomach; //, the heart, 



