271 
Nature of the Spongilla fi mbU’is. 
and Schweigger,— in different parts of Great Britian and Ire- 
land,— in France by Lamouroux ; and probably it has not 
been looked for on other continents. It grows abundantly in 
Lochend near Edinburgh, where I have procured all the speci- 
mens for the experiments and observations detailed in this me- 
moir ; it is seen covering the surface of many of the rocks and 
stones on the east side of the lake, and enveloping the wooden 
posts at the north end of it, when the water is low in autumn ; 
it spreads indiscriminately over every solid body it encounters, 
whether animal, vegetable, or mineral, and adheres so closely to 
them, that it cannot be separated without laceration. We ob- 
serve it more frequently, and better developed, on the over- 
hanging or perpendicular sides of solid bodies than on their 
acclivities or their summits ; this has relation to the position of 
certain large orifices on its surface, to be noticed hereafter. 
Though of a very delicate and brittle nature, it thrives on the 
most exposed ridges and prominent angles of rocks, which is 
probably owing to its usual depth from the agitated surface, 
and to the sheltered condition of small lakes, compared with the 
open sea, where the marine sponges thrive best on the sheltered 
sides of rocks. When young, it appears in small, round, convex 
spots, of a light grey coloured, soft, downy, substance, adhering 
to the surface of stones under water, or spreading irregularly as 
a flat woolly covering of a light greenish-grey colour, having a 
line or two of thickness, and an extension of one or two inches. 
But as it advances in growth, it becomes more compact in tex- 
ture, and of a darker sea-green colour, acquires a thickness of 
more than two inches, covers a continuous surface of several feet 
in length, sends up from every part of its surface irregular, short, 
compressed lobes, sharp ridges, thin laminae, or cylindrical, small 
branches, rounded at their extremities, and it presents numerous 
very distinct apertures, of different sizes, leading into its inte- 
rior. From the looseness of its porous surface and internal tex- 
ture, and from its mode of enveloping substances in the pro- 
gress of its growth, we generally find in its interior portions of 
sand, mud, or gravel, shells of fresh water testacea, fragments 
of roots or branches of trees, tubularise, larvae, particularly of 
phryganeae, innumerable animalcules, and different kinds of ova. 
s 2 
