SPONGES. 
QK 
\jO 
on any part of our shores that are left exposed by the sea 
at low spring-tide, without noticing irregular masses of 
yellow fleshy substance incrusting them, which rise into 
little conical hillocks perforated at the extremity, like the 
crater-cones of tiny volcanoes. This is the Crumb-of-bread 
Sponge (Ilalichondria panicect), one of our most common 
species ; and it is peculiarly suitable for displaying the 
currents of which we have been speaking (Plate II. fig. 2). 
Dr Grant remarks, that it presents the strongest current 
which he had seen. “Two entire round portions of this 
Sponge,” he says, “ were placed together in a glass of sea- 
water, with their orifices opposite to each other at the 
distance of two inches ; they appeared to the naked eye 
like two living batteries, and soon covered each other 
with feculent matter. I placed one of them in a shallow 
vessel, and just covered its surface and highest orifice 
with water. On strewing some powdered chalk on the 
surface of the water, the currents were visible at a great 
distance ; and on placing some small pieces of cork or of 
dry paper over the apertures, I could perceive them 
moving by the force of the current, at the distanco of ten 
feet from the table on which the specimen rested.* 
dho publication of these facts convinced naturalists that 
Dm gelatinous flesh of the Sponge exerted some vigorous 
action by which the currents were maintained, and cilia 
weie suspected to be the organs. But the closest scrutiny 
ailed to detect them, until first Dr Dobie, and then Mr 
ei bank, succeeded in seeing them in action in a living 
natn e Sponge. In similar situations to those where the 
rumb-of-bread Sponge occurs, may be found, but much 
* Edin. Phil. Joum., xiii. 104. 
