334> Dr Grant’s Observations on the Structure 
fices themselves, or on the contraction and dilatation of the ge- 
neral mass of the sponge, they could not fail to imagine that 
those orifices would exhibit a kind of systole and diastole corre- 
sponding with the exit and entrance of the water. Cavolini, in- 
deed, that profound and accurate observer, had not only seen 
the minute pores every where over the surface of the animal, 
but even conceived that the sponge was nourished by these su- 
perficial pores, as marine plants are. He was not aware, how- 
ever, of the currents which pass continually through the body of 
this animal, and imagined the fecal orifices to be mere accidental 
appearances, which are not met with on every sponge. As this 
circumstance of the want of fecal orifices on many sponges has 
been frequently alleged by naturalists, and even by Lamouroux, 
it may be proper to remark here, that, as currents of water pass 
through the body of every living sponge, from the surface to- 
wards the interior, the same currents are continually flowing 
from the interior to the surface by different passages ; and it is 
of little importance in the economy of this animal, whether the 
apertures by which the currents have their exit, be large and 
conspicuous, or minute and less easily observable ; every species 
of this genus must necessarily possess such orifices, great or 
small, for the discharge of its currents, its excrements, and its 
ova. 
In the Spongia compressa , and many tubular sponges, the 
currents pass in a perfectly straight line through their parietes ? 
from the external pores to the interior of their general cavity, 
which is always quite open at its pendent extremity. On laying 
open such sponges, we do not perceive, either on their internal 
or externa] surface, any large fecal orifices as we see on the ex- 
ternal surface of the Spongia officinalis; but if we examine the 
internal surface of their general cavity, we easily perceive that 
they have nearly as many small orifices for the exit of the cur- 
rents, as there are pores on the outer surface of their parietes for 
their admission. It is quite evident, that, in such sponges as the 
papillaris , cristata , panicea , &c. the same arrangement could 
not possibly exist ; for, as these animals spread over the smooth 
surface of cliffs, the currents cannot possibly find an exit on the 
surface opposite to that on which the pores are distributed, that 
surface of the sponge being completely shut up by the solid 
