256 J. G. WALLER ON CLIONA CELATA, ETC. 



out this close enquiry and investigation, it would be impossible 

 to accept any theory, which involves an acid secreted in the Sponge, 

 for any purpose whatsoever. Nor would an enquiry of this kind be 

 complete if it stopped at the Cliona. It must be pursued throughout 

 the several orders of the Sponges to ascertain the positive or nega- 

 tive proofs.* 



On a former occasion, I pointed out three different operations, that 

 have been suggested in the making of these burrows, viz., by acid, 

 soft living substance, or hard substance. These may be represented 

 by secretive powers, living sarcode, horny teeth, or the like. The 

 use of acid on all substances, as far as my experience goes, is 

 irregular in operation, unless carefully prepared against as in the 

 process of etching. Defined edges are otherwise impossible, and, 

 as to any rhythmical reproduction of the same form, it is absolutely 

 out of the question. In engraving, the etched line and that done 

 by the graver has a very different aspect under the microscope, and 

 shows what are the separate conditions between that executed by an 

 erosive material and that by a hard tool, even in working a fine line. 

 The one is irregular, the other is not. The exercise of a soft sub- 

 stance in boring would and must produce rounded edges. A hard 

 substance, but not exactly sharp, which grinds rather than cuts^ 

 may show a result somewhat irregular under the microscope, but it 

 will nevertheless be able to define and preserve sharp outlines and 

 boundaries of the tool's operation. And it will also show whether 

 the tool worked in a right line or in segments of circles. These are 

 the conditions I propose, in part, to consider with the object we are 

 discussing. 



But before I proceed to do this, it is well to cast a glance at such 

 analogies, which seem at least to justify a certain suspicion, if 

 nothing more, of the nature of the " borings " seen in shells of 

 molluscs, &c. What common operation is most familiar to us 

 which simulates the burrows in these shells ? Is it not that of a 

 Scolytas, a borer in wood ? I have an early printed book, dated 

 1484, the beechen covers of which are perforated throughout by 

 what has been called " the book-worm." So completely is it 

 burrowed, that, but for its leathern envelope it would scarcely hold 

 together. This is done by the minute larva of a beetle, which 

 infests beech and other woods with which books were originally 



* Of course I sol aside the action of carbonic acid, which belongs to the 

 process of respiration, «fec. 



