Mr. Hogg's Observations on the Spongilla fluviatilis. 369 



as brought forward by the first author may be learnt in perusing the ' Obser- 

 vations sur la Spongille i-ameiise {Spongilla ramosa, Lamarck ; Ephydatla la- 

 custris, Lamouroux), par M. Dutrochet,' " Annales des Sciences Naturelles," 

 p. 205. torn. XV., 1828. But the only notice I can find of M. Gervais's opinion 

 is contained in a very late paper by M. Dujardin, published in the second 

 series of the same Annales, torn. x. Zool. p. 11. And I should moreover re- 

 mark, that Baron Cuvier, in both editions of his "Règne Animal," has made 

 no mention of the Spongillœ, or Freshwater Sponges, and has expressly de- 

 scribed "les Eponges" as being "corps marins*." We must then conclude 

 that he had entirely overlooked them ; or, what is more probable, that he had 

 considered that they are plants, and therefore were not the subjects of his work. 



Dr. Johnston, as will be seen from his beautiful book entitled " A History 

 of the British Zoophytes," which has only just been given to the world, at 

 p. 28, still retains the same views on this subject as he did in the work to 

 which I have before referred. 



Next, it becomes me (however unwilling I may originally have been to en- 

 tertain such an opinionf) to state, that I now feel satisfied this species of 

 Freshwater Sponge is truly a plant, and not either a simple individual animal, 

 or a group of aggregated animals, or the structure or production of any animal 

 whatsoever. Many careful and repeated experiments upon different specimens 

 of the Spongilla Jiuviatilis have at length convinced me that such is the real 

 nature of it; and the results of those experiments I will here, as briefly and 

 clearly as I am able, detail to you. 



About seventeen months ago, I observed that the green colouring matter in 

 the River Sponge was occasioned by the action of light, because sand-coloured 

 or pale brown specimens gradually became green by being subjected to the 

 daylight, and more especially so when exposed to the full rays of the sun : 

 whilst, on the contrary, pale specimens, when confined in a dark place, or 



* Voyez Règne Anim. torn. iv. p. 88, edit. 1817 ; et torn. iii. p. 321, edit. 1830. 



t It is almost unimportant to remark tliat in my short catalogue of PoJyparia, published in my 

 " Sketch of the Natural History of the Vicinity of Stockton-on-Tees," Stockton, 1827, it will be|noticed 

 that I arranged the genera Spongia and Spongilla in my last order, Gelatinifera, of family 3. Creatoi- 

 dea, section ii. Composita. Since Dr. Johnston lias given the synonyms and references to that cata- 

 logue in his " Britisli Zoophytes," I may perhaps be excused for adding this note. 



3 c 2 



