CHAR A C TER/S TICS. 
5 2 7 
careful inspection, groups of minute pores will be seen perforating the meshes. 
The large holes at the summits of the craters are termed oscules, and the small 
ones on the general surface, pores. Ellis, who put some specimens in a glass 
vessel of sea water, wrote that “We could plainly observe these little tubes to 
receive and pass the water to and fro ”; and further, “ The sponge is an animal 
whose mouths are so many holes or ends of branched tubes opening on its 
surface; with these it receives its nourishment, and by these it discharges like 
the polyps its excrement.” Ellis’s observations were erroneous in one important 
point. The water always passes 
out of the large orifices, and is 
not passed in by them. It is 
true that while the torrent is 
gushing out of the centre of an 
oscule, there is a slight passive 
return current at the margin. 
Ellis attributed the current to 
the contraction of the walls of 
the canals. He found that the 
current continued in the absence 
of any worms or crustaceans in 
the body of the sponges. 
Our knowledge of sponges 
really begins in 1825 with the 
observations of Grant, who ex¬ 
amined a fragment of a living- 
branch of a branching-sponge. 
On bringing one of the large 
apertures on the side of the 
branch fully into view, he 
beheld this living fountain 
vomiting forth from a circular 
cavity a torrent of liquid matter, 
and hurling along in rapid 
succession opaque masses, which 
it strewed everywhere around. 
After many experiments, Grant convinced himself that a current flowed out of 
all the large orifices, and not into one and out of another. He also rubbed 
powdered chalk on the surface of a bread-crumb sponge, and saw particles which 
clogged the margins of the minute pores on the surface driven into the interior; 
and thereby demonstrated the passage of currents into the interior through 
the pores. The origin of the sponge-fountains was now traced. In all sponges 
currents of water pass into the body through pores, and out again by one or 
more ways different from those by which they entered. To ascertain the cause 
of the currents, it is necessary to examine the anatomy of the sponge. A thin 
skin, which can be peeled off, is separated from the body by numerous minute 
supporting pillars. On cutting into the sponge, large canals are seen passing down 
a, FLAGELLATED CHAMBER OP BREAD-CRUMB SPONGE, SHOWING COLLAR- 
CELLS ; b, FLAGELLATED CHAMBER OF FRESH-WATER SPONGE. 
(Both figures 1600 diameters.)—After Vosmaer. 
