80 THE SEA-SIDE AND AQUAEIUM. 



Ms muscular power. Then follows an expansion of 

 the neck, or upper part of the ventral border, from 

 whence the syphons protrude. This movement closes 

 the posterior portion of the valves below the hinge, 

 and brings their serrated points together. The next 

 act on the part of the animal, is to place his foot 

 firmly at the base of the hole. When leaning for- 

 ward, he makes a sweeping movement fully half 

 round the cavity, and pressing firmly upon the 

 umboes, which nature has strengthened for the pur- 

 pose by two curved teeth, fixed on the inside of the 

 valves. At this stage, he again reclines on his breast, 

 and tilting up the shell as much as possible, he 

 makes another motion round to his former position, 

 leaning upon his back. By these intricate move- 

 ments, which the Pholas appears to accomplish by 

 a contraction almost painfully strong, it opens the 

 rasping points of the valves. These execute a very 

 peculiar scooping movement at the base of the cavity; 

 and the animal having got so far, refreshes himself 

 for further exertion by a short rest. 



The foregoing observations were a great point 

 gained in my investigation of the terebrating habits 

 of this creature. It had begun to bore, there could 

 be no doubt of that. The next question was, How 

 long it would continue to do so, and would it bore 

 through the rock ? These questions were in no long 

 time satisfactorily elucidated. 



Just three days after the Pholas had begun its 

 operations, I saw that the water in the tank had. 



