102 H. GILBEETSON NOTES ON SPONGES. 



the Geologists' Association by Mr. H. M. Johnsoii, bears upon this 

 point. The author points out how a crop of sponges, invested with 

 their gelatinous flesh, and living at the bottom of a deep ocean, 

 might have been suddenly buried in a thick stratum of white mud, 

 consisting of the minute shells of Foraminifera ; that they would 

 then die, and that while in the process of decomposition an inter- 

 change of materials might take place — the nascent carbonic-acid 

 parting with its carbon in exchange for the silica of the silicate 

 of soda which sea-water is known to contain. To illustrate the 

 power possessed by decomposing organic matter, Mr. Johnson pro- 

 duced two tadpoles, or rather one and the remainder of a second. 

 The first had been placed in a solution of silica, and after the lapse 

 of a few hours was submitted to the action of nitric acid without 

 any apparent injury. The other, which had not been submitted to 

 the silicifying process before being placed in the nitric acid, was 

 instantly destroyed. 



From such observations as these it is inferred that during the 

 decomposition of the sarcode of sponges a similar interchange of 

 carbon and silicon may have taken place in the Cretaceous seas, 

 thus producing those flints which in this neighbourhood are almost 

 the only stones which we find beneath our feet, and which, as I 

 have already mentioned, we use for building, and also as a material 

 for making roads and paths. 



I regret very much that at this season of the year the fresh-water 

 sponges of our rivers and ponds are not in such a vigorous condition 

 as to admit of showing the process of inhalation and of exhalation 

 under the microscope, which I have had the pleasure of exhibiting 

 on many occasions since 1855, when I first found a small variety 

 in the moat surrounding Brickendon Bury, the history of which 

 my late friend Dr. Bowerbank has given in his " Further report 

 on the vitality of the Spongiadae," * wherein he describes at length 

 the opening and closing of the pores in Spongilla fluviatilis, and 

 the imbibition and ejection of the surrounding water. "In the 

 performance of these instinctive acts," he says, " Spongilla possesses 

 the same degree of control over these actions that I have described 

 in my former report as existing in the marine sponge." 



Siich a decided statement as this, attributing volition to sponges, 

 is very remarkable, and very likely to be received with scepticism, 

 but it is highly interesting to us, inasmuch as it is founded upon 

 the examination of a living sponge from our own neighbourhood. 



* 'Eeport Brit. Assoc, for 1857,' p. 121. 



