388 Mr. Hogg's Observations on the Spongilla fluviatilis, 



be seen dye the paper with permanent colours exactly after the same manner 

 as the green chromule of the Spongilla has done. But in order to let the re- 

 semblance be more conspicuous, 1 have also stained the paper (on the left 

 side) with the chromule from the leaf of Primula Sinensis, the chromule of a 

 common Conferva, and that of Chara vulgaris ; and having placed these 

 beside the stain derived from the colouring material of the River Sponge, 

 every one must be immediately struck with the similitude of their tints. In 

 fact, the chromule of the Conferva appears almost identical in colour with 

 that of the Spongilla. 



The fourth : if a green piece of this Sponge and any common leaves be 

 steeped in strong acid, the effects are likewise to all appearance very similar. 

 For instance, I took a living piece of the River Sponge of a bright green co- 

 lour, drained off the water, and poured some muriatic acid over it ; at first a 

 little effervescence took place over the whole surface of the specimen in con- 

 sequence of some calcareous matter having been deposited from the water 

 upon it ; next, the action of the acid began to dispel the green and to turn it 

 to a rusty or iron colour*, like as it does when applied to the green of fresh 

 leaves. The specimen then became very soft and pulpy, and losing its form, 

 put on after a further maceration the same appearance as that which arises 

 from a similar effect of muriatic acid upon the parenchymatous substance 

 and chromule of any green leaf. 



And the fifth, relates to the disengaging of gas, in all probability oxygen. 

 Whilst engaged in my experiments on the action of light upon the colour of 

 the Spongilla, I repeatedly observed those living specimens when placed in 



* As it is a well-known property in Chemistry, that the most common and powerful acids change 

 the blue colour of vegetables to red. If, therefore, such an acid be applied to the colouring matter of 

 the Blue Sponge (Spongia carulea), and the colour should thereby be converted to red, this would go 

 far in deciding the vegetability of that marine species. As also, alkalies mixed with blue vegetable 

 juices turn them green, it may easily be proved whether that change takes place in the colour of the 

 same Blue Sponge under the influence of an alkali. And I will merely mention, that it would be in- 

 teresting to try the effects of acids and alkalies upon the colours of the Red-wine Sponge {S. vinosa), 

 and of the beautiful Coral-red Sponge (S. corallina), and thereby likewise determine whether the reds 

 be not of a vegetable nature. In addition to these Sponges, other species of a purple and violet, and 

 of a reddish, rose-coloured and pink, are to be found on the coasts of the Mediterranean in the vici- 

 nity of Nice, as we learn from M. A. Risso's " Hist. Nat. des principales Productions de I'Europe 

 Mdridionale," tom. v. Paris, 1826. 



