COMMON OBJECTS OF THE SHORE. 333 



the openings, thus making two counter cur- 

 rents. 



The living animal of the sponge can, of course, 

 only be seen in the newly-gathered specimen. It 

 consists of a gelatinous, filmy substance, similar to 

 the white of an egg, and varying in quantity in 

 the different species. If a small portion of this 

 be placed under a microscope, it exhibits minute 

 transparent grains ; and yet this gelatinous sub- 

 stance, spread out upon the network, the skeleton 

 which itself has made, separates from the sea such 

 substances as shall nourish it, and serve for the 

 fabrication of its own peculiar structure. 



The opposing currents of water, during the 

 entire life of the animal, are described by Dr. 

 Grant as most rapid and remarkable. Having 

 brought one of the larger apertures of the Spongia 

 coalita under the microscope, this writer describes 

 it as " a living fountain, vomiting forth from a cir- 

 cular cavity an impetuous torrent of liquid matter, 

 and hurling along, in rapid succession, opaque 

 masses, which it strewed everywhere around;" and 

 after having watched this orifice at short intervals 

 for five hours, sometimes looking at it for a quarter 

 of an hour at a time, the stream was seen still to roll 

 on with a constant and equal velocity. Dr. Grant's 

 description of these fountains in the Spongia pani- 

 cea is no less striking. " Two entire specimens of 

 this sponge 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 the material they ejected. 

 I placed one of them in a shallow vessel, and just 

 covered its surface and highest orifice with water. 



