'EXCAVATORS. 367 



can be demonstrated that the burrows are made by a 

 hard, and not a soft, instrument, nor by a solvent, the 

 theory is also at an end, and its further prosecution 

 useless. These propositions I have endeavoured to 

 prove." ! 



Without venturing to determine how the operation 

 is performed, we must confess our inability to recognise 

 its impossibility, and, we may go still further, and 

 intimate our conviction that those who advocate the 

 boring theory have the better of the argument, and 

 that there are stronger presumptions in favour of the 

 boring being accomplished by the sponge, whether 

 the process is evident or not, than in the declaration 

 that it is impossible to take place. It may be a case 

 in which a person is quite justified in suspension of 

 judgment, but the evidence of the opposition is in- 

 sufficient to acquit the sponge of all complicity in 

 the transaction. Whether the boring is accomplished 

 by annelids or sponges, it is clear that an elaborate 

 system of excavation is performed by some marine 

 organism, and that this animal is deserving of recog- 

 nition in this place as an excavator. 



Mr. Waller, and those who think with him, may 

 say that " boring sponges " is only an hypothesis, but 

 there are some apposite remarks, by one who well 



1 " On the so-called Boring or Burrowing Sponge," by J. G. 

 Waller, in "Journal of Quekett Microscopical Club," vol. ii. 

 (1871), p. 269, and vol. vi. (1881), p. 251. 



