with some Remarks on the Nature of the Spongiae Marinae. 389 



the bright and powerful rays of the sun^ and while they were daily increasing 

 in their green tints, to be covered with a great number of bubbles ; thinking, 

 however, that they were only air-bubbles escaping from some insect, or some 

 molluscous animal or other, which so frequently lurks within the canals of the 

 Sponge, I carefully chose two or three fresh specimens that were entirely free 

 from any parasitical animal; I placed them in a dish of water, which was 

 frequently changed, and submitted them to the direct action of the light of 

 the sun, by allowing the brightest rays to enter through a glass window and 

 to fall directly upon them ; every day bubbles of gas continued to be disen- 

 gaged from these Sponges, but only in any considerable quantity when ex- 

 posed to the most luminous sunshine. Because plants in the solar light usu- 

 ally evolve oxygen, which is principally derived from the decomposition of 

 carbonic acid gas. I therefore naturally conceived that these bubbles of gas 

 were most likely mere bubbles of oxygen*, which are so commonly given out 

 by all plants when put under water and subjected to the same influence of 

 light, and that they might thus prove, in some measure, confirmatory of my 

 opinion as to the vegetable nature of this Sponge. 



But I must make a more particular statement respecting the currents of 

 water that have been noticed flowing into and issuing out from the interior of 

 the Spongilla, and which are analogous to those described by Professor Grant 

 and other authors, as constantly occurring in the Spongice Marines, and 

 esteemed by them the strongest evidences of their supposed animality. These 

 currents I have repeatedly observed in most living masses of the River Sponge, 

 and have proved their actual presence in various ways. My attention was 



* Since plants absorb carbonic acid gas, and exhale oxygen : but, on the contrary, animals absorb 

 oxygen and give out carbonic acid gas ; if these bubbles on the application of a proper test were proved 

 to be oxygen gas, this would fairly be conclusive of the Spongilla fluviatilis being a plant. Though, on the 

 other hand, if these bubbles be chemically found nitrogen (azote), this would not decide the present 

 species to be an animal, because it has been lately shown (by Dr. Daubeny in the Phil. Trans, for 

 1836, and still more recently by Mr. Rigg in the Phil. Trans, for 1838,) that even plants, in certain 

 stages and under certain circumstances, not unfrequently evolve nitrogen. And if in such case we 

 can determine by means of chemical tests, that this Sponge actually decomposes carbonic acid gas 

 under the influence of solar light, we should then have arrived at a safe conclusion respecting its vege- 

 tability. Surely similar chemical experiments might be instituted to demonstrate the true nature of 

 the Marine Sponges. During the time I was making the experiments detailed in the text I had no 

 opportunity of proving these questions. 



