` Mr. Hoac'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 rameuse (Spongilla ramosa, Lamarck ; Ephydatia la- 
custris, Lamouroux), par M. Dutrochet, * Annales des Sciences Naturelles," 
p. 205. tom. 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, tom. x. Zool. p. 11. And I should moreover re- 
mark, that Baron Cuvier, in both editions of his “ Régne Animal," has made 
no mention of the Spongille, 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 opinion) 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 fluviatilis 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 Régne Anim. tom. iv. p. 88, edit. 1817; et tom. iii. p. 321, edit. 1830. 
+ It is almost unimportant to remark that in my short catalogue of Polyparia, 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 has given the synonyms and references to that cata- 
logue in his “ British Zoophytes," I may perhaps be excused for adding this note. 
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