103 
Functions of the Sponge. 
which has a glistening or membranous surface, with very few a- 
pertures, exhibits a powerful stream ; while the Spongia oculata y 
Spongia ocerampelina, and Spongia pdlmata , which have a more 
open woolly surface, propel their discharge to a shorter distance 
from their numerous circular apertures. 
On attempting to examine some of the larger flat species, as 
the Spongia panicea and Spongia cristata , in the same manner 
with the microscope, I found it not so practicable. The dissection 
necessary to reduce them to a smallness fit for examination un- 
der that instrument, and in a watch-glass, threw open the canals 
so much as to destroy their means of manifesting a concentrated 
current. But a single papilla torn from a Spongia papillaris , 
or other spreading sponge, which has the papilla much elevated, 
shows distinctly the current flowing constantly from it, when 
placed in a watch-glass with sea- water under the microscope. 
From the distinctness of the currents seen by this means, I 
was induced to try whether they might not be perceived by the 
naked eye, although they had escaped the observation of so 
many naturalists, and particularly of Montagu, who states, in the 
Memoirs of the Wernerian Society, that he could not perceive 
these currents, even with the assistance of a glass. On placing 
a fresh placentiform mass of the Spongia panicea in a glass of 
clear sea-water, I could distinctly perceive, with the naked eye, 
particles propelled to the surface of the water from a large cir- 
cular orifice in the centre of the mass. I afterwards placed a 
portion of the Spongia cristata in a shallow vessel, and covered 
it to the depth of half an inch with water. The orifices along the 
ridges at that distance from the surface, created a current there 
visible to the naked eye, and particles of dust floating on the 
surface of the water were drawn into the stream, and carried to 
the distance of two or three inches from the apertures. I sus- 
pended a Spongia compressa by its pedicle, in its natural 
position, with its aperture downwards ; and even in this small 
animal I could perceive a languid current issuing, and opaque 
particles occasionally propelled. The currents from this species 
are best examined by the microscope, but still are comparative- 
ly languid : this sponge has a vilious surface, and very large 
apertures, which are circumstances generally accompanying a 
weak current. 
