J. G. WALLER ON CLIONA CELATA, ETC. 255 



channel and not in the other. The theory of washing out has been 

 suggested, where the Sponge is not found at all, and is most con- 

 venient, but this will not answer where it has not filled the burrow. 

 We may, perhaps, be told it has retracted. I know what power 

 Sponge has of retraction, and have watched it in the living state, not 

 only of Spongilla, but of marine specimens on the rocks at 

 Paignton, but no retraction, such as is observable in the Sponge, 

 can possibly account for empty burrows. 



In presenting before you the result of the literature of the 

 subject, I must now notice the theory of Mr. Charles Stewart And 

 tli;Te is no one whose opinion, as such, is deserving of more respect 

 and attention, and, if this were a question of physiology, I should 

 have no place before him ; fortunately, it is of a very different 

 character. This, as far as I understand it, is, however, in some 

 respects, only the resuscitation of an old one, viz., that acid plays 

 a part ; with this important difference, that he goes to some analogy 

 to support his views, which is the action of lactic acid upon bone. 

 And he seems to infer, from this operation, a similar action in the 

 Sponge. Of course, given certain premisses, this theory has a plausible 

 possibility. Yet, it is open to doubt whether a theory, founded on 

 what is seen in special conditions of the human body, can be in 

 analogy to the living action of a lower creature. For the 

 gap is immense between the top of the Metazoa and an organism 

 which, at best, must be placed at the bottom. But herein lies the 

 difficulty. To concede a premiss is to concede a conclusion. It is 

 the old story, a theoretic and not a practical solution. It is a sug- 

 gestion to account for a conclusion already arrived at. There is, as 

 far as I see, no direct induction ; it is simply an idea, extremely 

 ingenious, of the application of which no proof whatever is given. 

 I oppose such a process of reasoning as unsound, even if the result 

 should establish that the " idea " is correct. 



If the acid theory be maintained, we must infer some secretive 

 powers in the animal's tissues. Then, it may be necessary to 

 maintain, that these powers belong only to the species Cliona, 

 one of the simplest in organization, in many particulars, of 

 the genus to which it belongs, and not to Sponges in general. 

 Surely this would be an assumption, which could not be received 

 without, at least, something like proof. There are re-agents 

 by which the presence of acid may be detected. There is the 

 spectrum analysis, by which some aid might be given ; but with 



