266 J. G. WALLER ON CLTONA CELATA, ETC. 



with renewal of its structure. How this can, by any possible 

 reasoning, be said to be analogous to what might take place by a 

 living thing acting upon a substance foreign to itself, i.e., the shell 

 of a mollusc or limestone rock, is to me inconceivable. It would be 

 very different, if we were discussing an action within the mass 

 of the Sponge ; it then might appear much more plausible. 



But the analogies, extremely interesting as they are, still are not 

 close, even in the forms of operation. There is a general resem- 

 blance, but it is irregular and incomplete, just as it is also in 

 iridescence of ancient glass, which Mr. Stewart also brought 

 forward as an analogy, though how it bears on the question it is 

 difficult to see, any more than in other similar forms of decomposi- 

 tion. Then only a small part of the phenomenon is accounted for 

 at best. 



It was advanced by Mr. Priest, on tlie authority of a passage 

 written by Mr. Carter, that the Sponge had been found to have 

 worked its oscula through the overlapping frond of a Nullipore. The 

 passage runs thus : " Cliona corallinoides not only excavates shells, 

 but the sandstone rock too of this locality, where it shelters itself 

 under the florid expansion of Melohesia lichenoides which goes on 

 growing (that is spreading in all directions), while the Cliona, 

 every here and there, makes holes through this crust or thalloid 

 frond for its pore areas or vent as required."* If the writer of the 

 above has not watched and seen -the whole of this operation, it is 

 nothing more than a deduction from appearances, of which there are 

 so many in the scientific history of this Sponge. Oscula projecting 

 through a crust of polypidoms are common enough, but give no 

 proof whatever of the Sponge being the factor ; the difficulties in 

 the way of such interpretation I have already stated. 



That the Sponge is parasitic can be shown by many examples in 

 my possession. It seeks seclusion in orifices or fissures between 

 incrustations, deserted tubes of Serjmlce, and can often be found to 

 be spreading over surfaces without excavation. (PI. XXI., Fig. 3). 



The limestone pebble from Babbicombe is a test object, as the 

 total absence of any Sponge in its deep-seated burrows is surely 

 fatal to the theory. Its curiously minute orifices are paralleled in 

 excavations in the shells of some oysters, as in example given 

 (PI. XX., Fig. 12), and it suggests the probability of more than one 

 species of factor. 

 * " Annals and Magazine of Natural History,*' 4th Series, Vol. viii., p. 15. 



