OF THE NATURE OF SPONGES. 45 



and satisfactorily shewed that the water was alternately 

 sucked in and expelled from them. This observation was 

 likewise made at the same time by several of my friends 

 to whom I pointed it out. Whether the contractile power 

 belongs to the spongy substance which forms the basis of 

 the tubes, or to the gelatinous crust A\ith which it is co- 

 vered, I could not of course ascertain : probably however, 

 to the latter. 



" Although perhaps we should not place too much de- 

 pendence upon chemical analysis in questions of this sort, 

 yet I think it is a fair analogical argument in favour of 

 the animal nature of sponges, that their chemical composi- 

 tion is wholly on that side of the question."* 



In 1825 Mr Gray forsook his first opinion, and became 

 a convert to the animality of sponges, which, with Lamarck, 

 he now acknowledged to be " true corals, nearly allied to 

 Antipathes and Gorgoniae." This conversion was occa- 

 sioned by the discovery that the spicula consisted wholly 

 of pure silica, — the quantity appearing, as might be ex- 

 pected, to be in proportion to the density of the fibres of 

 the sponge. Now he learned from Ellis's description of 

 the Gorgonia Briareus that spicula undoubtedly similar 

 composed its axis or bone — facts which proved " a conside- 

 rable afl&nity to exist between the sponges (both the ma- 

 rine and fluviatile) and the Gorgoniae, which latter are 

 known to be the habitation and production of individuals 

 belonging to the animal kingdom."! 



* Zoological Journal for June 1824, vol. i. p. •lOS See also Kirby's 



Bridgevvater Treatise, i. p. IG4. 



t Annals of Philosophy : New Series : ix. p. 432. — Mr Gray is now of 

 opinion that the animal nature of sponges is not " distinctly made out.'" 

 Syn. Brit. Mus p. 57. 



