104 Dr Grant’s Observations on the Structure and 
The Spongia panicea presents the strongest current which 1 
have yet seen, and has the greatest thickness of body of any 
spreading sponge which I have met with on the rocks of this 
part of the Frith of Forth, Two entire round portions of this 
sponge were placed together in a glass of sea-water, with their 
orifices opposite to each other, at the distance of two inches ; 
they appeared to the naked eye like two living batteries, and 
soon covered each other with feculent matter. I placed one of 
them in a shallow vessel, and j ust covered its surface and high- 
est orifice with water. On strewing some powdered chalk on the 
surface of the water the currents were visible at a great distance, 
and on placing some small pieces of cork or of dry paper over 
the apertures, I could perceive them moving, by the force of the 
currents, at the distance of ten feet from the table on which the 
specimen rested. A portion of soft bread, pressed between the 
fingers into a globular form, with a diameter larger than that of 
the orifice, and placed over it, was not moved away in a mass by 
the stream, but was gradually worn down by the current beat- 
ing on its sides, and thus propelled to a distance in small flakes. 
A portion of unburnt black-coal, with twice the diameter of the 
orifice, was instantly rolled off the mouth of this living fountain, 
in whatever position I attempted to make it rest upon it- A glo- 
bule of mercury, of equal diameter with the orifice, let fall upon 
it through a glass tube was not removed or shaken, and complete- 
ly stopped the current. I now pierced, with a needle, a thin su- 
perficial canal, in the vicinity of the closed orifice, and established 
a new current, which continued, even after removing the obstruc- 
tion from the original orifice. 
A globule of mercury, of any smallness, placed over the ori- 
fice of a living sponge, is too heavy to be affected by the small 
column of water which impels against its smooth round surface, 
flowing at the rate with which it issues from that orifice, and is 
useful in enabling us to stop up the currents of certain orifices, 
in order to direct the stream with greater force through a parti- 
cular aperture, which we wish to examine through the micro- 
scope. By adopting this plan with a healthy Spongia panicea^ 
which has generally very few and large orifices on the surface, 
we can distinctly perceive, with the naked eye, that the current 
never enters by the same apertures through which it issues, and 
