281 
Nature of the Spong’dla friabiiis. 
might be the external appearance or age of the spongilla, or 
the part of the lake from which it was procured. The curves 
of the spicula have a relation to the rotundity of the canals and 
openings* and their sharp points relate to their function of de- 
fending these passages. The whole arrangement of the spicula, 
around the canals, shows that these are not accidental passages, 
formed by worms or aquatic insects in a vegetable substance, 
and helps to prove, that its currents are not produced by any 
foreign intruders, though this substance is infested with myriads 
of ciliated animalcules, which are constantly producing currents 
to attract their prey. In place of the phosphate of lime of the 
higher orders of animals, or the carbonate of lime of the lower 
orders, we have seen that silica is the earthy matter of the ske- 
leton of this zoophyte. The same is the case with most of the 
British marine sponges, and with some zoophytes which possess 
polypi. This earth is secreted by many plants, but I am not aware 
that it has been observed in the form of symmetrical, tubular spi- 
cula, composing the axis of any substance in the vegetable king- 
dom. 
By a little agitation in water, the gelatinous matter of the spon- 
gilla resolves itself almost entirely into minute, pellucid, green- 
coloured granules, which have a singular tendency to reunite. 
When allowed to remain for a few hours at rest, they unite into 
a compact, dark green, velvety membrane, perfectly resembling 
the Oscillatoria viridis , Vauch. and attach themselves to the bot- 
tom of the vessel. When a few of them are placed in a watch- 
glass with water, they form themselves into minute spheres, be- 
ing constantly rolled to and fro by the animalcules, from which 
it is nearly impossible to free this substance. The minutest of 
the granular bodies, when viewed through the microscope, are 
seen to have a distinct power of locomotion. Their slow motions, 
in this separate state, are probably produced by the same organs 
which they employ to produce the currents, when attached to 
the sides of the canals. The soft matter of the spongilla does 
not seem to possess a distinct membranous coat, but is a little 
more consistent, and has a glistening surface, wherever it is in 
contact with the element in which it lives, as within the canals, 
and on the outer surface of the body. We observe minute por- 
tions of the gelatinous matter assuming naturally a spherical 
