ON POLYPI. 589 
stratum, which is the seat of sensibility and life. Olivi tells 
us that there are species of sponges, which present three very 
distinct substances. 1. The fibrous matter which forms the 
support, or as it were, the skeleton of the sponge. 2. The 
mucous gelatinous substance, surrounding the fibrous parts; 
and 38. A terrene matter, mingled with the preceding, and 
forming a sort of cortical substance, which surrounds the ge- 
latine itself. According to Father Vico, however, the organi- 
zation of the sponges is much more complicated, and he would 
fain discover in them, a muscular and a nervous system, ova- 
ries, seminiferous vessels, &c. As this opinion, however, 
seems wholly untenable, it is unnecessary to dwell on the de- 
tails on which it is founded. Olivi, whose opinion is more 
probable, regards the fibres, not as very important organs, but 
as the support, or frame-work of the living body, and the sort 
of marrow, which is sometimes found in their interior, he sup- 
poses to have originated at the period when the animal was 
young. He thinks that the mucilaginous and cortical enve- 
lope really constitutes the animal, but that this animal is 
amorphous. : 
Sponges are considered by M. de Blainville, after Pallas, 
Cavolini, Olivi, Donovan, &c., as organized bodies, interme- 
diate to the two organic kingdoms, without any regular deter- 
minate form; presenting an absorbent surface having some 
obscure traces of feeling, nourished by the molecules from the 
surrounding medium, pretty nearly like vegetables. Repro- 
duction takes place by a sort of pullulation, or scission of the 
living or gelatinous matter. 
The sponges are always adherent to submarine bodies, of 
whatsoever nature they may be, at variable, though always 
considerable depths, and consequently, in places where the 
sea is tranquil. They are particularly to be found in great 
abundance in the excavations of rocks. It is certain, however, 
that some species can exist in places covered and left bare 
