130 ^ BRITISH SPONGES : 



which I do not question, the examination I had made some time 

 since of the Cliona induced me to believe that it was a member 

 of the genus Halichondria, and this suspicion became more con- 

 firmed after I had procured Mr M'CoUa's specimens, for there 

 can be no doubt whatever of the identity of the production in 

 the two states described. On communicating this opinion to my 

 friend Mr Edward Forbes, I learned that he had arrived at the 

 same conclusion ; and after an examination of some portions of 

 a massive specimen, Mr Bowerbank also agrees with us. " The 

 structure of the animal," Mr B. writes me, " is so much in ac- 

 cordance with that of many species of British Halichondriae that 

 I have examined, that I cannot conceive it to be any thing but a 

 true sponge, and that Dr Grant has been deceived by some pa- 

 rasite into the belief of its having true polypes as part of its ori- 

 ginal structure. I cannot but think that it is more likely that 

 the Doctor, with all his known accuracy, should be mistaken 

 than that so wide and essential a difference should exist between 

 Cliona and Halichondria as that one should have polypes and 

 the other be totally without them ; and the existence of polypes 

 in my idea would lead us to imagine quite a different arrange- 

 ment of the parts of the animal from that where it was never 

 designed by nature that they should exist." 



The conjecture that the polypes, evidently ascidian, observed 

 by Dr Grant, may be parasitical is not improbable, for, on a pe- 

 rusal of his history, it may be remarked that, in the very many 

 experiments made by him, they were seen twice only, and their 

 organic connection with the spongious mass is not distinctly 

 made out. The currents as described too resemble those of the 

 other sponges but not those produced by polypes, for in the lat- 

 ter the cm*rent is generated in the circumfluent water and invari- 

 ably flows inwards along one side of the tentacula while an out- 

 ward current sets up the opposite side, and the water neither 

 flows out of nor enters within the body. The distribution of the 



