338 Dr Grant's Observations on the Structure 
experiments of this kind, 1 have never been able, by any irri- 
tation of a fecal orifice, to accelerate or retard, in the slight- 
est degree, the velocity of the current, which issues from it. 
I have frequently reclined upon the rocks, both at Preston- 
pans Bay and at Leith, during the recess of the tide, and have 
watched attentively, with the naked eye, and with the assistance 
of magnifying powers, the fecal orifices of a great variety of 
sponges, while still growing, uninjured, on their native seats ; 
but neither in those which were under the surface of the sea, 
nor in those which paved the bottom of limpid pools, nor in 
those which the tide had left uncovered, could I ever detect the 
slightest motion of the fecal orifices. In these situations X have 
irritated and punctured the vicinity of the orifices with a needle, 
and have touched them with nitric and muriatic acids, and they 
have, notwithstanding, remained perfectly motionless. 
The fecal orifices of the branched species seem to be equally 
inactive, as in those which spread over the surface of rocks. I 
suspended several living branches of the common Spongia di - 
chotoma , and of the Spongia oculata , and Spongia ocerampelina , 
separately, in glasses of clear sea- water, and observed attentive- 
ly, through the sides of the vessels, the round orifices, ranged 
along the outer margins of the branches, but could not perceive 
them change their dimensions, in the smallest degree, although 
their currents and feculent discharges were distinctly seen. On 
piercing the woolly surface of these branched sponges with a 
needle in the neighbourhood of the orifices, they did not enlarge 
or diminish their diameters ; a whitish chalky matter came out 
from the punctured places of these sponges, and diffused itself 
quickly through the water. 
I cut off’ an entire prominent papilla from the Spongia urens ; 
and after placing it in a watch-glass, with clear sea- water, I look- 
ed down, through the straight orifice of this isolated papilla, with 
a powerful microscope ; but though particles of matter were dis- 
tinctly seen, propelled upwards from the aperture, it was not 
perceived to change its caliber, or exhibit the slightest motion 
of any kind. This papilla, with a wide passage extending di- 
rectly through its axis, when placed on its side, under the mi- 
croscope, shewed a current passing out at both its open extremi- 
ties. I may here remark, that on all papillae which I have 
