Linncean Society. 459 



In the latter portion of this letter the author endeavours (in addi- 

 tion to what has been already stated at p. 58) to demonstrate the ve- 

 getahility of the river sponge, from the following facts, which were 

 obtained by many experiments made by him upon that substance 

 during the last two summers. 



1 . From the general resemblance of the membrane which invests 

 the soft portion or jelly with the membrane or cuticle of the leaves 

 of many plants. 



2. From this gelatinous or soft portion being so similar to the pa- 

 renchymatous substance of the more fleshy kinds of leaves, and be- 

 ing, like the latter, chiefly composed of numerous pellucid globules. 



3. From the green colouring matter or chromule contained in those 

 globules, on being pressed out, giving a permanent green or yellow- 

 ish-green colour to white paper, as is the case with the chromule of 

 leaves and plants. 



4. From strong acids having the same effects on this sponge as 

 they are seen to have upon plants when they are macerated in them. 



5. From the mode in which numerous bubbles of gas, most pro- 

 bably oxygen, are disengaged from the surface of the living mass of 

 Spongilla, when exposed to the brightest solar light, being so ex- 

 tremely analogous to that which is known to occur with the leaves 

 of a plant when immersed in water and submitted to the direct ac- 

 tion of the light of the sun. 



As to the currents of water which take place in the Spongilla flu- 

 viatilis, and are so similar to those which have been noticed by Dr. 

 Grant and other authors in the sea sponges, and relied upon by them 

 as the best evidence of their supposed animal nature, Mr. Hogg 

 has, after many careful experiments, never been able to witness them 

 taking place in any specimens which have been entirely destitute of 

 every parasitical insect or other animal ; he therefore concludes that 

 these currents are caused by some insect, or crustacean, or moUus- 

 can, which is seen so generally to inhabit nearly every specimen of 

 the Spongilla ; and by means of the animal's performing the function 

 of respiration, the streams or currents of water are found to enter 

 into and flow out from the pores or oscules of that structure. But 

 if on future investigations it shall be proved that these currents do 

 occur in such individual masses of the Spongilla fluviatilis as are 

 quite free from every parasite, Mr. Hogg would then consider that 

 they are eff'ected by the same agents as cause the motions or circu- 

 lation of the fluids in vegetables, and most probably by an endos- 

 mosis and exosmosis of difl*erent fluids, in accordance with the im- 

 portant discoveries of M. Dutrochet. 



