1839.] Linnean Society. 37 



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

 tion to what has been already stated at p, 8,) to demonstrate the ve- 

 getability 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 

 parenchymatous substance of the more fleshy kinds of leaves, and 

 being 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. 



4. From strong acids having the same eff'ects 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, 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 investigation 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 effected by the same agents 

 as cause the motions or circulation of the fluids in vegetables. 



The author has not perceived any trace of animal organization, or 

 the least symptom of sensation, or any powers of contraction and di- 

 latation in this species of sponge, although he has applied to it, when 

 in a fresh and vigorous state, several sorts of powerful stimuli. 



