Dr Grant’s Observations on the Structure of the Sponge. 95 
without lacerating or injuring their bodies. Although they 
thrive best in the sheltered cavities of rocks, they come to ma- 
turity in situations exposed to the unbroken fury of the surge ; 
but, in the latter situations, I have always observed them smal- 
ler and firmer in their texture like those inhabiting colder cli- 
mates, whether their exposure were to the north or south. They 
cover the nakedness of cliffs and boulders, they line with a varie- 
gated and downy fleece the walls of submarine caves, or hang 
in living stalactites from the roofs. 
They attach themselves indiscriminately to bodies belonging 
to the mineral, vegetable, and animal kingdoms, and the indi- 
vidual species seem to have no law with regard to the particu- 
lar substances to which they adhere. I have found sponges ad- 
hering to basalt, greenstone, sandstone, soft slate-clay, various 
kinds of fuci, shells of living and of dead moJlusca , shells of 
living crustaceous animals, Sertidaria , Flustra , Corallines , and 
even to the soft surface of living compound Ascidice ; but I 
have not seen them on clay, sand, gravel, bituminous shale, de- 
cayed wood, nor any metallic body, though favourably placed to 
receive them. 
The branched species I have always found hanging perpen- 
dicularly from the under and sheltered surface of solid over- 
hanging cliffs, or tabular masses of rock. The flat spreading 
species with projecting papilla, I have generally found on the 
sides of boulders ; while the flat species, without prominent pa- 
pillae, are generally seen on the under-surface of rocks, or en- 
veloping bodies which admit of a little motion by the agitation 
of the sea. The delicate and beautiful Spongia compress a I 
have found hanging from the surface of Ascidia , or of flat spon- 
ges, which covered the under-surface of rocks : they hang either 
single or attached in groups, and are likewise seen attached to 
the rock itself. The Spongia coalita is a branched species, 
capable of rising erect, from the great breadth of its base, the 
firmness of its skeleton, and the frequent anastomoses of its 
branches. 
The known range of magnitude of the sponge is perhaps 
greater than that of any other animal; indeed, it is one of the 
most irregular of organized beings in magnitude, form, and 
colour. The Spongiw compressa of the Frith of Forth some- 
