144 
ON THE FRESH-WATER SPONGE. 
and consist of spiculse of one-two-hundred-and-fiftieth to one-two-hundredth of a 
millimeter in breadth, on the ends of which are seated very beautifully-formed 
disks of one-fiftieth M. in diameter. These little disks are more or less strong at 
the edges, and always rather regularly notched; and if they lie free for a long 
time, each tooth extends itself from the edges of the disk into long points, four 
or five, but mostly seven or eight, of which are formed, ultimately doubling 
themselves into tolerably regular hook-formed spiculse. The surface of the 
gemmules of Spongilla is clothed with the silicious bodies above described, and 
they are seated with the external side of one disk firm upon the membrane of 
the gemmule, whilst the disk at the other end of the spiculse extends itself more 
or less over the surface of the thick crust ; and the spiculse themselves, which 
are all placed vertically upon the surface, become enclosed by the chalky mass of 
the crust, and are more visible the thinner the crust. The disk by which the 
spiculse on the surface of the membrane is fastened, is quite plain; and the 
spiculse stand so near one another, that they are almost always indented one with 
the other by the crenated borders of the disks, and upon a surface of the circum¬ 
ference of a quarter of a millimeter from 2,000 to 2,500 of these silicious bodies 
present themselves. A great number of these bodies can easily be preserved for 
separate inspection, if the gemmules are previously boiled in a mineral acid. 
The Chalk-mass between these bodies exhibits exceedingly small four-, five-, and 
six-sided figures, as if there were present a cellular structure, similar to that which 
I have described in the Winter gemmules of Alcyonella stagnorum. 
Each of the gemmules of Spongilla has a little round spot where the crust is 
absent, and where it apparently opens when the contained embryo is born; but 
at .the beginning of January of this Winter, the contents are still of such a 
nature that it is impossible to predict what will take place. When the gem¬ 
mules are passed, there appears a thick whitish substance, which consists of little 
bright globules, and larger balls of an equal circumference and circular form ; on 
these balls or larger globules an exceedingly delicate mucous membrane is 
observed, which encloses the entire bundles of smaller globules, but on the 
slightest touch is destroyed. If these balls are placed between two glass-plates 
and pressed slowly, the larger globules are broken down into much smaller 
molecules, which exhibit an exceedingly active molecular motion. But what 
will be formed from these contents of the Spongilla-gemmules, the observations of 
a future period must point out. 
In the substance of Spongilla lacustris , besides the ordinary silicious spiculse, 
externally beautifully-formed silicious bodies present themselves, and which I 
have observed from one-sixteenth to one-tenth of a millimeter in length; there 
are also spiculse of excessive delicacy, which are clothed upon their surface with 
a great number of little pointed excrescences, which become longer with increasing 
