34 



LIFE, IN ITS LOWER FORMS. 



body. But whither goes this current 1 The pores lead 

 into large channels, which also run through the body, like 

 the drains from individual houses, which run into the 

 main sewers ; and these open on the exterior of the body 

 by more or less conspicuous orifices called oscula, or mouths. 

 From these latter the effete water is poured in forcible 

 streams, and thus a circulating current is maintained. 



It was Dr Grant who first established the fact of this 

 current from personal observation. His account of the 

 discovery is full of interest. " I put a small branch," he 

 observes, " of the Spongia coalita, with some sea- water, into 

 a watch-glass, under the microscope, and, 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 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 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 with a constant and 

 equal velocity." The vehemence of the current then began 

 to diminish, and in about an hour ceased.* 



No one can have looked with any attention at the rocks 



* Edin. Phil. Joum. xiii. 102. 



