> ^■ 



Animal Nature of Spo)7grs. * 203 



cable, than to the opii\ions now entertained of the fresh-water 

 spongoid bodies. They are like Polonius's cloud ; a camel, a 

 whale, or m hat you please. Mr. Gray gives an account of some 

 observations on one of these fluviatile productions, which, from 

 his description, I should fully agree with him in considering a 

 true vegetable; he speaks of the little greenish granules which 

 were washed out of the substance, and which soon after grew 

 " entirely after the manner of vegetables," and having the appear- 

 ance of the genera of Algae. '*" I have very little doubt," says Mr. 

 Gray, " that if the mucilaginous substance of the marine sponge 

 be examined, it will be found to contain similar grains; but not 

 having the opportunity of going to the sea side since making the 

 above observation, I have not been able to verify my idea." 



No longer ago than last autumn, being on the Dorsetshiie coast, 

 I examined the structure of recent marine sponge with care, and 

 certainly discovered no traces of the granules described by Mr. 

 Gray (and which, in fact, already formed one of the generic 

 characters of Spongilla, according to Lamarck). One very im- 

 portant fact however I have ascertained, and that is the power of 

 contraction and dilatation in the tubes of which this substance Is 

 composed. I placed a piece of sponge, immediately after it was 

 taken from the sea, in a glass of sea-water; a little dust had 

 settled upon the surface, and upon looking attentively at the 

 water, the regular alternate motion and rest of the dust upon the 

 surface, immediately over the mouths of the tubes, most dis- 

 tinctly and satisfactorily shewed that the water was alternately 

 sucked in and expelled from them. This observation was like- 

 wise made at the same time by several of my friends to whom I 

 pointed it out. Whether the contractile power belong to the 

 spongy substance which forms the basis of the tubes, or to the 

 gelatinous crust with which it is covered, I could not of course 

 ascertain : probably however to the latter. 



Although perhaps we should not place too much dependance 

 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 composition is wholly on that side 

 of the question. 



o 2 



