DITBLIN ITATUBAL BISTORT 80CIBTT. 141 



Tying both In shape and colour. On examination It could be plainly geen that the 

 organ called a tube was nothing more than a thin membrane which the animal 

 could coil or roll up like paper, and over which it exercised as complete control 

 as the elephant over his trunk. It has been supposed that it is through the in- 

 strumentality of this organ that locomotion is performed ; but if my view of the 

 animal being a stone-borer is correct, this cannot be its use ; the animal must 

 be stationary, from its position in the stone, and, consequently, the organ is used 

 merely for the purpose of capturing its prey or food, whatever that may be. 

 When I had satisiiud myself as to what the animal truly was, it struck roe that 

 it would add greatly to the interest of its history if I could establish the fact of 

 its being a stone-borer. I was aware that it might be objected to this view, that 

 the animal merely occupied the cavity made by some other of the Lithodomi; but 

 the very first view I had of the animal convinced me that such was not the case, 

 for, as 1 stated before, I found it impossible to remove the animal through what 

 may be termed the neck of the cavity ; however, to satisfy myself further ou the 

 subject, I again applied my hammer to a recently thrown up stone, which solved 

 the problem to my satisfaction. I found four or five specimens in this stone, and 

 I distinctlpr traced from the surface of the stone to the animal a passage, nar- 

 row and smuous, but equal in breadth through its length (about an inch), and 

 through which the animal projected its tube at pleasure ; the excavation then 

 suddenly increased to the size of the animal, in the form of a cone, into which 

 the animal accurately fitted. Now, if you examine the cavity formed by Hiatella 

 rugosa, it will be seen that it assumes the form of a pear, suddenly swelling out 

 from the point where the animal first entered the stone until it completes its 

 chamber. I consider that I have given sufficient proof to remove all doubt as to 

 its being in its economy a stone-borer, and that its tube is most wonderfully 

 adapted in its construction to supply the animal with all necessary food from the 

 surrounding waters ; moreover, I should say, if it were not encased in its stony 

 apartment it would easily fall a victim to its enemies, as it is scarcely possible 

 to coaceive a more helpless and defenceless creature. It may be proper here to 

 give some explanation as to the mode bv which the Lithodomi excavate into the 

 stone. The theory adopted by the earlier writers on zoology was, that the ani- 

 mal secreted an acid which acted on the limestone, and thus enabled the animal 

 to make its passage into the stone, and subsequently to enlarge it, as the animal 

 increased in size ; but modern chemistry has demolished this very plausible ex- 

 planation, by showing that no sugh acid existed either in the animal or in its 

 secretions ; and, consequently, that was not the agency by which the operation 

 was performed. The theory now adopted by the most eminent zoologists is, that 

 the tongue being armed with sharp siliceous particles, and kept in constant mo- 

 tion, wears away the stone by the friction, the animal during this process accu- 

 rately fitting itself into the cavity ; and the proof adduced in support of this view 

 is, that on anatomical examination being made, it is found that the tongue is 

 thus armed, and, moreover, that it is an organ of great strength and power in 

 addition. On subjecting the matter, or residuum, found in the cavity, after re- 

 moving the animal for examination, it is found to consist of two substances — a 

 limestone powder mixed with those siliceous particles. The inference drawn 

 from this fact is, that they have been rubbed off by the friction used, and mixed 

 together. As this theory satisfies such eminent men as Alder and Uandcock, it 

 would be rash to call the accuracy of it into question ; but of this I am certain, 

 that in the many examinations I have made into the cavities of the Lithodomi, I 

 never could detect the slightest remains of such residuum ; neither do 1 think 

 the animal could exist with it in the cavity, a perfectly smooth surface being an 

 indispensable ingredient to the well-being of the animal. A slight examination 

 will satisfy you as to this. Look to the inner surface of any shell, univalve, or 

 bivalve — could it be more smooth? Examine the sides of the cavitv made by 

 the Lithodomi, and you find that it is polished as finely as if from the hands of a 

 statuary. The necessity of this internal polish was so well known to LinnsBoa 

 that ho suggested an artificial mode of manufacturing pearls, by scratching the 



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