50 Gray on Sponges. 



has not seen the polypes, and appears to have been only lead to 

 that conclusion by a false analogy from his having examined dried 

 specimens, and there has only been two affinities pointed out with 

 regard to the animal, the one just noticed, and the other by Blain- 

 ville^ which I have remarked on, while they have the general ap- 

 pearance and structure of many marine algae ; and if the marine 

 and the freshwater agree in their manner of growth, there is little 

 doubt but that they must be removed to the vegetable kingdom.* 

 Walking one day on the bank of the Thames, when the tide was 

 very low, I observed a quantity of a green substance on the shore 

 far from the bank, just above Kew bridge, which on examination 

 proved to be a freshwater sponge ; having collected a considerable 

 quantity I brought it home, when on putting it in water a num- 

 ber of green granules were washed out, which came more plenti- 

 fully when the sponge was squeezed, and left only a light coloured 

 very brittle fibrous substance ; there were a few partly decayed 

 leaves at the bottom of the basin, on which the green granules fell. 

 Being called away I left them there for a day or two, when on my 

 next examination I found they had formed a more velvety mass, 

 through which visible fibres were shooting, which gradually en- 

 larged, thus growing entirely after the manner of vegetables ; the 

 granules were very minute, and I thought had all the appearance 

 of the genera of Algae. 



I have very little doubt that if the hiucilaginous substance of 

 the marine sponge be examined, it will be found to contain similar 

 grains, but not having the opportunity of going to the sea side 

 since making the above observation, I have not been able to verify 

 my idea ; I hope, however, that some person near the coast will 

 examine the fact, so as to settle this long doubtful point, and thus 

 greatly assist the possibility of arriving at a natural arrangement, in 

 which either the introduction of an heterogeneous body, or the ab- 

 sence of an analogue, is the object of great consideration. But 



* Especially Ulva diaphana, which has been considered as an Ulva by many, 

 as Fucus by Hudson, and sponge by Parkinson, and as alcyonium by Gmelin,- 

 &c. with a description o^iis polypi ; but lately formed into a genus by Lampn- 

 roux under the name oi Alcyonidiwn ; it certainly has no polypes, for I found it 

 in abiuidance at Sheerness. 



