64 OPINIONS AND DISCOVERIES 



the pores and oscules one with another, along which the 

 water finds a ready coiu-se or circulation, and affords nu- 

 triment to all the inner parts of the masses ; with locomo- 

 tive sporules ; and in some species with fixed sporidia." * 

 Mr Hogg then proceeds to prove, by the testimony of se- 

 veral naturalists, the sameness of these sporidia in marine 

 and fluviatile sponges ; and he combats the argument for 

 their animality, drawn from their chemical analysis, by 

 showing that there exists in them no one principle which 

 is not also to be found in certain vegetable substances, 

 while the discovery of iodine in the sea sponges determines 

 that they more neai'ly resemble the Fuci. f He sums up 

 the evidence of their want of animal life in this sentence : 

 — " They have no tentacles, no cilia, no mouth, no oeso- 

 phagus, no stomach or gastric sac, no gizzard, no alimen- 

 tary canal, no intestine, no anus, no ovaria, no ova, no mus- 

 cles or muscular fibres, no nerves or ganglia, no irritabi- 

 lity or powers of contraction and dilatation, no palpitation, 

 and no sensation whatsoever. Surely, then, we cannot any 

 longer esteem these natm'al substances to be individual ani- 

 mals, or even groups of animals, in which not one organ, or 



• Lin. Trans, xviii. p. 400-1. Lotsd. 1840. 



f Dr Andrew Fyfe, who first discovered iodine to be a constituent of 

 sponge, asks, " May not the fact, that sponge contains iodine, be an argu- 

 ment in favour of the opinion of Linnaeus, that this substance properly 

 belongs to the vegetable world, class Cryptogamia, from the plants of 

 which iodine is obtained." But he adds, " it appears that the iodine con - 

 tained in sponge, is in a different state of combination from what it is in 

 the other substances, as in the former it is not soluble in water, while it is 

 so in the latter." Edin. Phil. Journ. i. p. 257-8. Edin. 1819 ; and 

 xiii. p. 199. The argument, rendered suspicious by this circumstance, 

 is now valueless, for iodine has been detected in cod-liver oil. Edin. 

 Med. and Surg. Journ. liv. p. 251 ; Brit, and For. Med. Rev. x. p. .558- 



