232 B. W. PRIEST ON THE NATURAL HISTORY 



cells having a hyaline collar protecting the flagellum. These latter 

 cells line all the passages leading from 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 Sj^onge. (Fig. 1, 

 Plate XVII.) 



Some naturalists, I believe, look upon the collared cells as playing 

 the part of respiratory organs only, and not as means for assimilating 

 nutriment, at any rate I have no doubt, along with others, with re- 

 gard 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 per- 

 forates the investing membrane. (Fig. 5, Plate XVII.) 



The late Professor James Clarke, of Kentucky, was the first to 

 notice the analogy of these ciliated cells with the free flagellate col- 

 lared Infusoria, followed up at the present time by the elaborate re- 

 searches of Mr, Saville Kent. It has been found by this gentleman 

 that some of the free collared monads are identical with the ciliated 

 collared monads discovered in the Spongiadge, each separate collar- 

 bearing cell possessing a separate existence, and securing its nutri- 

 ment in the same manner. Furthermore, Mr, Kent tells us that 

 Sponge structure may be and is built up from one of these constituent 

 monads, by a repeated process of cleavage, by which means it quickly 

 multiplies itself, though still more rapidly by the subsequent encyst- 

 ment and breaking up of the monads into spores. 



Through the kindness of Mr. Charles Stewart I have been enabled 

 to see for myself these truly wonderful collared cells, in sections of 

 Grantia compressa and G. ciliata, properly prepared. Fig. 3, Plate 

 XVII., is a sketch of a section through one of the passages leading 

 to the cloacal cavity of the first-named species, showing them in 

 situ. You will often see an embryo Sponge in a greater or less state 

 of development, and dispersed through the sarcode the ama?boid par- 

 ticles or cytoblasts ; also the supposed stinging threads, analogous 

 to those found in the freshwater Hydra. 



Professors Ilaeckel and Huxley, I believe, still hold that the proper 

 })lace of the Sponges is among the Coelenterata, including the Sea 

 Anemones and Hydroid Zoophytes, from the theory of their being 

 composed of separate multicellular membranes or tissues The recent 

 investigations with regard to their place amongst the Protozoa may 



