Mr. Harper having termed the boring organ of the Pholas the "hyaline stylet," found it to have puzzled some of the disputants, whereupon Mr. Harper writes:--"Its use up to the present time has been a mystery, but the general opinion of authors seems to be, that it is the gizzard of the Pholas. This I very much doubt, for it is my belief that the presence of such an important muscle is solely for the purpose of aiding the animal's boring operations. Being situated in the centre of the foot, we can readily conceive the great increase of strength thus conveyed to the latter member, which is made to act as a powerful fulcrum, by the exercise of which the animal rotates--and at the same time presses its shell against and rasps the surface of the rock. The question being asked, 'How can the stylet be procured to satisfy curiosity?' I answer, by adopting the following extremely simple plan. Having disentombed a specimen, with the point of a sharp instrument cut a slit in the base of its foot, and the object of your search will be distinctly visible in the shape of, if I may so term it, an opal cylinder. Sometimes I have seen the point of this organ spring out beyond the incision, made as above described." Lastly, Mr. Harper presented the Editor of the "Athenæum" with a piece of bored rock, of which he has several specimens. He adds, "On examination, you will perceive that the larger Pholas must have bored through its smaller and weaker neighbour (how suggestive!), the shell of the latter, most fortunately, remaining in its own cavity." Now, Mr. Robertson claimed for his observation of this phenomenon novelty and originality; but Mr. Harper stoutly maintained it to be "as common to the eye of the practised geologist as rain or sunshine." The details are curious; though some impatient, and not very grateful reader, may imagine himself in the condition of the shell of the smaller Pholas, and will be, as he deserves to remain, in the minority.[29] It may be interesting to sum up a few of the opinions of the mode by which these boring operations are performed. Professor Forbes states the mode by which Molluscs bore into wood and other materials is as follows:--"Some of the Gauterspods have tongues covered with silica to enable them to bore, and it was probably by some process of this kind that all the Molluscs bored." Mr. Peach never observed the species of Pholas to turn round in their holes, as stated by some observers, although he had watched them with great attention. Mr. Charlesworth refers to the fact that, in one species of shell, not only does the hole in the rock which the animal occupies increase in size, but also the hole through which it projects its syphons.