404 Mr. Hogg's Ohservat'iom on the Spongilla fluviatilis, 



des plantes marines donnaat par Tincineration, des odeurs et des produits 

 analogues a ceux des aniniaux*." Neither is the presence of ammonia in 

 these substances at all conclusive of their animal nature ; for I have before 

 mentioned that some plants contain nitrogen or azote, and from the combi- 

 nation of this ingredient with hydrogen the ammonia itself is formed ; where- 

 fore in those vegetables, especially in the lower water-plants, which contain 

 nitrogen, more or less of ammonia is known to be generally produced. 



Thus it seems that there really exists no more peculiarity in the chemical 

 composition of Spongesf, than what is also present in that of certain vegeta- 

 ble substances. And for the sake of corroborating this, I will cite the follow- 

 ing authority from a naturalist, equally illustrious in botany and in zoology, 

 who, describing Sponges as animals, nevertheless allows, " chymicis etiam 

 principiis paul6 similiores plantis deprehenduntur;}:." 



To me then it is evident, that the Sea Sponges being so perfectly analogous 

 in every part of their structure with the Freshwater Sponges, it is impossible 

 that they can be separated from one and the same natural order, or accounted 

 as the one pertaining to the animal kingdom, and the other to the vegetable. 

 And as I have become convinced that the River Sponge is a true member of 

 the latter, and as I have endeavoured so to demonstrate this in the preceding 

 pages of my present letter, I must now necessarily be compelled to acknow- 

 ledge myself a convert to the vegetability of the Sea Sponges. In the full 

 confirmation of this, and in the absence of more direct proofs, which may yet 

 be derived from future researches on these marine productions, whilst growing 

 in their native localities, I will concisely sum up in a general manner the fol- 

 lowing evidence of their want of animal life, or what I may term their non- 

 animality. They have no tentacles, no cilia, no mouth, no oesophagus, no 

 stomach or gastric sac, no gizzard, no alimentary canal, no intestine, no 

 anus, no ovaria, no ova, no muscles or muscular fibres, no nerves or ganglia, 



* Hist, des Polyp. Corall. Flex., p. 12. 



t But the discovery of iodine in the Sea Sponges determines that they more nearly resemble the 

 Fuci in their chemiceJ composition. Consult the article " lode" at p. 594. torn, xxiii. of the Diction- 

 naire des Sciences Naturelles (Paris, 1822), which was written by M. Chevreul, Professor of Chemistry. 

 — I only became acquainted with this fact on December 7th, 1839. J. H. 



X Dr. PaUas in Elench. Zooph., p. 376. 



