116 THE MECHANICAL FUNCTIONS. 



that power of contraction which had, for so many ages, been 

 ascribed to it.* 



Dr. Grant has also shown the true nature of the currents 

 of fluid issuing at difTerent points from the surface of these 

 animals, as well as the absence of all visible movements in 

 the orifices which give exit to the fluid. Never did he find, 

 in his experiments, the slightest appearance of contraction 

 produced in any part of the sponge, by puncturing, lace- 

 rating, burning, or otherwise injuring its texture, or by the 

 application of corrosive chemical agents. Of his discovery 

 of the fluid currents, he gives the following interesting ac- 

 count: " I put a small branch of the Spongia coalita, with 

 some sea-water, into a watch-glass, under the microscope, 

 and, on reflecting the light of a candle through the fluid, 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 fountain, vomiting forth, 

 from a circular cavity, an impetuous torrent of liquid matter, 

 and hurling along, in rapid succession, opaque masses, which 

 it strewed every where around. The beauty and novelty of 

 such a scene in the animal kingdom, long arrested my atten- 

 tion, 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 direction, 

 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 w^ith 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 



• See his papers on this subject in the Edinburgh Philosophical Journal, 

 vol. xiii. p. 95 and 333, fi"om which most of the facts mentioned in the above 

 account are taken. 



