105 
Functions of the Sponge. 
we might thus measure the whole strength of the forces employ- 
ed to produce the currents in any particular specimen. 
But as the Spongia cristata was the kind in which Mr Ellis 
imagined he saw the water pass to and fro through the same a- 
pertures, I placed, in a glass of clear water, a portion of this 
sponge, which consisted of a single ridge, with a range of pro- 
jecting apertures along its vertex, and on examining, for some 
time, with a pocket lens, each of the apertures in succession, 
through the transparent sides of the vessel, I found that they 
all sent forth a constant and uninterrupted stream of water from 
the interior of the animal, with occasional discharges of opaque fe- 
culent matter. In order to be still more satisfied that none of the 
apertures were destined to receive or inhale water, while others 
propelled it from the animal, I placed under the microscope a 
small branch of the Spongia coalita , on which there were only 
three apertures, and I found that, however long I watched 
them, they were always employed in conveying water from the 
interior. But as it was still by no means impossible that, while 
my attention was fixed on one aperture which discharged water, 
another, which I had just quitted, might now be inhaling that 
fluid, I took from the rocks some specimens of the Spongia com - 
pressa , constructed like a small white paper bag, with only one 
round aperture at the extremity of the body ; and on placing 
each in succession under the microscope with sea-water, I found 
that these animals sent forth from the only aperture of their 
bodies a slow but constant stream. 
It thus appears, that the round apertures on the surface of 
a living sponge, are destined for the conveyance of a constant 
stream of water from the interior of the body. This stream 
conveys away the particles of excrementitious matter constantly 
separating from the interior of the canals, and which are not 
only seen, by the assistance of the microscope, constantly issu- 
ing from the apertures, but are even perceived by the naked 
eye propelled occasionally in flakes ; and when a portion of any 
kind of living sponge is allowed to remain for a day at rest, in 
a white vessel filled with the purest sea-water, accumulations of 
feculent matter are always seen immediately under each orifice. 
The feculent matter of the Spongia palmata , Spongia ocuXata , 
and Spongia ocerampelina , consists of a very fine dark-brown 
