SPONGES. 151 



chus Zoophytorum ;'' whence it was copied by 

 succeeding authors, and the error became at 

 length so widely disseminated, that for more 

 than half a century it was received as an es- 

 tablished fact in natural history. The elaborate 

 and accurate researches of Dr. Grant on these 

 subjects have at length dispelled the prevailing 

 illusion, and have clearly proved that the sponge 

 does not possess, in any sensible degree, that 

 power of contraction which had, for so many 

 ages, been ascribed to it.* 



Dr. Grant has also shown the true nature of 

 the currents of fluid issuing at different points 

 from the surface of these animals, as well as the 

 absence of all visible movements in the orifices 

 which give exit to the fluid. Never did he find, 

 in his experiments, the slightest appearance of 

 contraction produced in any part of the sponge, 

 by puncturing, lacerating, burning, or otherwise 

 injuring its texture, or by the application of 

 corrosive chemical agents. Of his discovery of 

 the fluid currents, he gives the following inte- 

 resting account : "I put a small branch of the 

 Spongia cocdifa, with some sea-water, into a 

 watch-glass, under the microscope, and, on re- 

 flecting the light of a candle through the fluid, 



* See his papers on this subject in the Edinburgh Philosophical 

 Journal, vol. xiii. p. 95 and 333, from which most of the facts 

 mentioned in the above account are taken. 



