122 TOILERS IN THE SEA. 



the pores, in most cases to the cloacal cavity, or 

 cavities, to the oscula, regulating the currents of water, 

 and causing them to flow through the channels, and 

 convey the nutriment necessary to the existence of 

 the sponge. Some naturalists, I believe, look upon 

 the collared cells as playing the part of respiratory 

 organs only, and not as means for assimilating nutri- 

 ment ; at any rate, I have no doubt, along with 

 others, with regard to their regulating the currents of 

 water. In some species of sponges these ciliated cells 

 occur only in well-determined circular chambers, with 

 their ciliated ends pointing towards the centre, each 

 chamber having a small aperture, which perforates the 

 investing membrane. The late Professor James 

 Clarke, of Kentucky, was the first to notice the 

 analogy of these ciliated cells with the free flagellate 

 collared infusoria, followed up at the present time by 

 Mr. Saville Kent. It has been found by this gentle- 

 man that some of the free collared monads are 

 identical with the ciliated collared monads discovered 

 in the sponges, each separate collar-bearing cell 

 possessing a separate existence, and securing its 

 nutriment in the same manner. Furthermore, 1 Mr. 

 Kent tells us that sponge structure may be, and zs, 

 built up from one of these constituent monads, by a 



1 "A Manual of the Infusoria," by W. Saville Kent, p. 143, 

 and following. London, 1880. 



