OF THE NATURE OF SPONGES. 49 



pieces of cork or of dry paper over the apertures, I could 

 perceive them moving, by the force of the currents, at the 

 distance of ten feet from the table on which the specimen 

 rested. A portion of soft bread pressed between the fin- 

 gers into a globular form, with a diameter larger than 

 that of the orifice, and placed over it, was not moved away 

 in a mass by the stream, but was gradually worn down by 

 the current beating on its sides, and thus propelled to a 

 distance in small flakes. A portion of unburnt black-coal, 

 with twice the diameter of the orifice, was instantly rolled 

 off" the mouth of this living fountain, in whatever position 

 I attempted to make it rest upon it. A globule of mer- 

 cury, of equal diameter with the orifice, let fall upon it 

 through a glass tube was not removed or shaken, and com- 

 pletely stopped the current. I now pierced, with a needle 

 a thin superficial canal, in the vicinity of the closed orifice, 

 and established a new current, wliich continued, even after 

 removino; the obstruction from the original orifice. 



" A globule of mercury, of any smallness, placed over 

 the orifice of a living sponge, is too heavy to be affected 

 by the small column of water which impels against its 

 smooth round surface, flowing at the rate with which it is- 

 sues from that orifice, and is useful in enabling us to stop 

 up the currents of certain orifices, in order to direct the 

 stream with greater force through a particular aperture, 

 which we wish to examine through the microscope. By 

 adopting this plan with a healthy Spongia panicea, which 

 has generally very few and large orifices on the surface, 

 we can distinctly perceive, with the naked eye, that the cur- 

 rent never enters by the same apertures through which it 

 issues, and we might thus measure the whole strength of 



