278 
Dr Grant on the Structure and 
with, and almost imbedded in, the glistening matter lining the ca- 
nals, and they assist, by their natural curvatures, in giving a 
roundness to these passages. The fecal orifices, in this species, 
are never raised to the extremities of projecting papillae, and 
have no regularity ot form, size, or distribution. They may be 
compared with those of the Spongia panicea, preferring to open 
on the deeper parts of the surface ; and, like that sponge, this 
substance thrives best where its free surface hangs down in a 
vertical position, as when it spreads on the overhanging sides of 
rocks, or on the under surface of wooden planks. 
From this striking resemblance in structure and general ap- 
pearance between the spongilla and the marine sponges, a re- 
semblance which probably I would never have detected in this 
soft substance, without adopting every precaution which expe- 
rience had shewn to be necessary in the examination of the lat- 
ter zoophytes, I was naturally led to expect the same currents 
through its internal canals which are so obvious and well known 
in the true sponge. The shaking of this brittle zoophyte in 
carrying portions of it from the lake to be examined under the 
microscope in my apartment, injured so much the organization 
of its soft parts, as to baffle my first attempts to discover its cur- 
rents. At length, however, I succeeded by examining portions of 
it on the side of the lake, the instant they were cut from the 
rocks. On placing an entire portion of it perpendicularly in a 
glass of clear water, and in perfect rest, I observed, with a lens, 
through the sides of the vessel, not only particles of matter 
driven with rapidity from the large openings between the lobes 
and ridges, but likewise floating particles distinctly drawn in 
through the lesser openings, distributed on the elevated parts of 
the surface. I afterwards succeeded several times in preserving 
such portions of it as had lobes or branches projecting from their 
surface, so entire as to exhibit their currents in my apartment for 
nine hours, after their removal from the rocks. On cutting ofl* 
these uninjured lobes, and placing them successively under the 
microscope in a watch-glass with rain-water, I observed the same 
regular and constant streams from the small fecal orifices placed 
at different distances along their surface, the same feculent mat- 
ter accompanying the streams, and the same motionless state of 
the mass during their flow, which are observed in the marine 
