340 Dr Grant’s Observations on the Structure 
motionless. I have tried to excite its orifices to contract, by ir- 
ritating them with sharp instruments, by letting fall drops of 
corrosive acids in their immediate vicinity, and by touching the 
apertures themselves with a red-hot wire, but always without 
success. 
In crder to ascertain whether there might be any systole 
and diastole, or other motions, taking place within the orifices, 
in the course of the great canals, I observed steadily, through a 
pocket-lens, a globule of air, which I had caused for that pur- 
pose to appear at one of the orifices of the Spongia cristata. 
Such globules make their appearance at the orifices of a living 
sponge, when it has been lifted out of the water for a short time, 
and is again plunged into it, when its canals are partially emp- 
tied. The globules of air thus included in the canals by the sur- 
rounding water, generally advance with a slow progress to the 
margins of the orifices, being pushed on by the advancing cur- 
rents behind, and escape to the surface of the water, to allow a 
free passage to the stream. It must be obvious, that, if there 
were any systole and diastole of the lips of the orifices, or any 
contractions and dilatations of the parietes within the canals, or 
any such motions of the general mass of the animal, they would 
have been manifested by the successive advancing and retreat- 
ing of the globule of air at the orifice of the canal. It did not 
retreat, however, nor palpitate in the slightest degree, but con- 
stantly advanced with a slow and equable motion, till it escaped 
from the aperture to the surface of the water. I raised this 
portion of sponge a little out of the water, and placed a single 
globule of mercury over one of the orifices. While I observed 
the globule steadily through a magnifying glass, I irritated the 
papilla with a- red-hot wire, but did not produce any motion of 
the orifice or papilla, for the mercury was not observed to rise 
or sink. A small lively branch of the Spongia coalita was 
placed in a watch-glass, with some sea-water under the greatest 
magnifier of the double-reflecting microscope. The spicula pro- 
jecting and converging around the orifice to defend it, were 
magnified into large, transparent, pointed crystals, and the cur- 
rent from the circular orifice looked like an eruption from the 
crater of a volcano ; but though attentively watched for a quar- 
