SPONGES. 



35 



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 (Halichondria panicea), 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 distance of ten 

 feet from the table on which the specimen rested.* 



The publication of these facts convinced naturalists that 

 the gelatinous flesh of the Sponge exerted some vigorous 

 action by which the currents were maintained, and cilia 

 were suspected to be the organs, But the closest scrutiny 

 failed to detect them, until first Dr Dobie, and then Mr 

 Bowerbank, succeeded in seeing them in action in a living 

 native Sponge. In similar situations to those where the 

 Crumb-of-bread Sponge occurs, may be found, but much 



* Edin. Phil. Joura., xiii. 104. 



