and Functions of the Sponge . 848 
the parched deserts of Arabia, are observed to fill themselves 
completely with water when in contact with that element, and to 
retain it for a long time undiminished. If, in this condition, 
they are but slightly pressed on the surface with the finger, the 
water with which their internal canals are filled, starts at once 
from several fecal orifices, in such a manner as would lead one 
at first to suppose, that the effect was produced by some effort 
or trembling of the animal. This, however, is entirely a me- 
chanical effect, resulting from the elasticity of the strong horny 
spicula which bound the canals, and prevent them from chan- 
ging their dimensions, or emptying themselves during the absence 
of the tide. And when we attempt to tear these sponges from 
the rock, we feel a much more powerful resistance than could 
naturally be expected, from a substance so soft and elastic. 
This resistance might very easily be mistaken for a shrinking of 
the animal, but arises entirely from the mechanical structure of 
its skeleton ; for, though the spicula which compose it are soft, 
flexible, and elastic, they are not susceptible of being stretched, 
and they are bound together at their points of contact, by a very 
strong ligamentous opaque matter, equally incapable of exten- 
sion, as we see in the Spongia communis , which we are constant- 
ly handling for domestic purposes. When we attempt, there- 
fore, to stretch the living animal beyond a certain extent, the 
soft gelatinous matter escapes from every pore, and the animal 
either slips quickly from our grasp, into its original position on 
the rock, or yields so suddenly by breaking, as to make it appear 
as if it had been resisting by some voluntary contractile effort. 
The property of contracting when touched, had been so uni- 
formly observed in animals low in the scale, and seemed so ne- 
cessary to their functions and self-preservation, that few among 
the ancients ventured to call in question its existence in the 
sponge. But as no one had ever distinctly observed such a mo- 
tion in this substance, its real existence became very generally 
questioned by the botanists of more recent times ; and particu- 
larly by those who devoted their attention to the study of ma- 
rine plants. Bay, Tournefort, Boerhaave, Marsigli, Linnaeus, 
Spallanzani, and nearly twenty naturalists of eminence during 
the last century might be quoted, who regarded the sponge as 
a vegetable, and destitute of contractile power. But the nume- 
