m 
and Functions of the Sponge. 
branch, although the currents continued unaltered. On pour- 
ing off the water, I let fall a drop of nitric acid on the middle of 
this single branch ; the corrosive poison sunk like water into the 
body of the animal, and, though again watched for five minutes, 
there was no perceptible shaking, or bending, or shortening of 
the sponge ; nor could I observe any shrinking or depression on 
the place where the acid fell ; that place of the branch quickly 
assumed a milky-white colour, while the rest retained its natural 
bright straw-yellow colour. When the coalita is young, its 
branches are long and slender ; they shoot in all directions to 
seek for points of attachment, and adhere to, or envelope, every 
thing they meet with, living or dead, animal, vegetable, or mi- 
neral; wherever the branches cross or touch each other they 
form a perfect union ; sometimes the animal spreads as a layer 
over an oyster-shell, or covers a rock like a convoluted bush, or 
like the root of a fucus, or forms a cement, connecting into a mass 
all manner of shells, stones, or broken glass ; sometimes it forms 
an irregular mass, with a perfectly smooth surface, without any 
point of attachment, rolling to and fro, at the mercy of the waves. 
As it advances in life, its colour assumes a darker shade, with a 
tinge of brown ; it becomes less smooth on the surface ; loses its 
translucency ; and its fibrous part predominates, as the hard parts 
of other animals predominate progressively from birth to decay. 
After storms, or during the dredging season, irregular branched 
masses of it are left at low water, along with the spatangus, and 
many other interesting animals, on the extensive sands of Mus- 
selburgh. I have frequently repeated the above experiments on 
the coarse, rough branches of the adult coalita , but with the same 
result ; the acid seems partially to dissolve the part, and renders 
it at length more transparent. 
I next took a portion of the Spongia urens , which formed a 
covering of nearly an inch and a half in thickness around a 
large stem of the Fucus palmatus or digvtatus. It had been torn 
from the rocks in deep water, and was left on the sands by the 
retiring tide. Being perfectly entire, and uninjured, and some 
feet in length, I plunged its thickest extremity into a basin of 
water, to observe its currents, and touched the immersed surface 
with the finger, but no kind of contraction or trembling motion 
were perceptible ; no dimple formed at the part touched. Ha- 
ving raised the immersed part a little from the water, after two 
