48 OPINIONS AND DISCOVERIES 



sponge depends upon its flow inwards, while the outward 

 cui'rent carries off the excrementitious matter, as seems 

 proved by the fact that particles of this description always 

 pollute the outflowing water, however clear and pure it may 

 have been sucked in ; and the ova are likewise carried out 

 of the body by the same means. * It was no doubt the ob- 

 servation of these cmTents, imperfectly noted, which misled 

 Marsigli, Ellis and Bell, into the belief of a motion of sys- 

 tole and diastole in the orifices of the sponge, and an alter- 

 nate flux and eflBux of the water through them ; and Mon- 

 tagu failed to detect the phenomena from employing mag- 

 nifiers of too small a power, or from being unaware of the 

 mode of examination by which they can be made visible 

 to the naked eye. " The Spongia panicea," says Dr Grant, 

 " presents the strongest current which I have yet seen, and 

 has the greatest thickness of body of any spreading sponge 

 which I have met with on the rocks of this part of the Frith 

 of Forth. Two entire round portions of this sponge were 

 placed together in a glass of sea-water, wdth 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 feculent matter. I placed 

 one of them in a shallow vessel, and jiLst covered its sur- 

 face and highest orifice with water. On strewing some 

 powdered chalk on the surface of the water the currents 

 were visible at a great distance, and on placing some small 



and it is of little importance in the economy of this animal, whether the 

 apertures by which the currents have their exit, be large and conspicuous, 

 or minute and less easily observable ; every species of this genus must 

 necessarily possess such orifices, great or small, for the discharge of its 

 currents, its excrements, and its ova." Vol. supra cit. p. .'5.')4. 

 * Lib. cit. p. 103-6. 



