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



or eyen by the same factor. However different, in some respects, in 

 arrangement between the limestone burrow and those of the oyster- 

 shell, the modus operandi is identical, and there is no escape from 

 whatever conclusion this forces upon us. The creature who makes 

 the one makes the other, be it Sponge or Annelid. 



I must now return to the borings of the Scolytus, and present you 

 with the analogy of the operations. For it is surely a natural 

 mode of reasoning to proceed from the known to the unknown, for, 

 as no one can doubt the evidence of his eyes as to the analogy 

 presented in external appearance with those in oyster-shells, &c., 

 or indeed with the burrows themselves, the comparison is a fit one to 

 lead us on to the solution of the interesting question in debate. 

 (Vide PI. XX, Figs. 1, 3, 4, 6.) Now to the microscope, and let 

 us see how far this assists in the enquiry. 



Here is a drawing, made under the microscope, showing the mode 

 of excavating by the larvse of the Scolytns (Fig. 9). And what does it 

 teach us ? Why exactly the same principle, the difference is only in 

 the material. There is the same concentric cutting as in the shell and 

 the pebble ; the same law of operation. The mode of excavation is 

 sub-circular in its process, such as is familiar to us in the work of 

 mandibles moving laterally. The conclusion is therefore irresistible, 

 that creatures of similar faculties made all the borings in question ; 

 creatures armed with teeth or jaws, call them by what names you 

 please — larva or annelid. Can it possibly be asserted that a Sponge 

 does precisely the same thing ? 



And now what are the difficulties in the way of such a solution ? 

 Do they exist at all ? The voracious larvge of many of the 

 Articulata are borers, as we know. Many of the Annelid^e, at least, 

 are acknowledged to be so too. Not only so now, but have been so 

 in far back geological epochs. The Spiroglyphus and other exca- 

 vators in shell belong to the Tertiary period, and ages still more re- 

 mote, and furnish some indications of their presence.* And an analogy 

 drawn from the operations of a larva of one of the Insecta in a class 

 but little elevated above the Annelid, closely allied in form and 

 habit, and all belonging to the same great group of Articulata, is 

 surely more natural than one drawn from an operation in a mammal, 

 especially as the latter has got to be proved in detail. 



Then where is the difficulty in assigning to the Sponge, which 



*» Mr. Etheriflere, the President of the Geological Society, very kindly sent 

 uie a list of Annelidao referred to. 



