152 THE MECHANICAL FUNCTIONS. 



I soon perceived that there was some intestine 

 motion in the opaque particles floating through 

 the water. On moving the watch-glass, so as to 

 bring one of the apertures on the side of the 

 sponge fully into view, I beheld, for the first 

 time, the splendid spectacle of this living foun- 

 tain, vomiting forth, from a circular cavity, an 

 impetuous torrent of liquid matter, and hurling 

 along, in rapid succession, opaque masses, which 

 it strewed everywhere around. The beauty and 

 novelty of such a scene in the animal kingdom, 

 long arrested my attention, but after twenty-five 

 minutes of constant observation, I was obliged 

 to withdraw my eye from fatigue, without having 

 seen the torrent for one instant change its direc- 

 tion, or diminish, in the slightest degree, the 

 rapidity of its course. I continued to watch the 

 same orifice, at short intervals, for five hours, 

 sometimes observing it for a quarter of an hour 

 at a time, but still the stream rolled on with a 

 constant and equal velocity." About the end of 

 this time, however, the current became languid, 

 and, in the course of another hour, it ceased 

 entirely. Similar currents were afterwards ob- 

 served by Dr. Grant in a great variety of species. 

 They take place only from those parts that are 

 under water, and immediately cease when the 

 same parts are uncovered, or when the animal 

 dies. 



It thus appears that the round apertures in 



