REPORT ON THE CALCAEEA. 1 ."> 



Let us imagine a sponge (e.g., a Sycon) under its usual conditions. The cilia of the 

 flagellated cells are in movement, and the water enters through the pores into the radial 

 tubes in order to make its way to the osculum ; let us pursue the direction taken by a 

 particle coming through the pores into the Sponge. If such a particle, having entered 

 the radial tube, be constrained to follow the most rapid course of the water, viz., that 

 in the middle of the tube, it is evident that it will reach the gastric opening of the tube 

 without any contact with the flagellated cells ; now, if precipitated by the whirlpool 

 occasioned by the cilium of the next flagellated cell in an oblique direction towards the 

 wall of the tube, the possibility is not excluded that, following this direction, it will 

 reach the comparatively slow current of the water close to the flagellated cells, and be 

 taken in by one of them ; but, even though this may happen, such an issue cannot occur 

 very often, for the comparatively slow flowing of the water near the surface of the wall 

 is of a somewhat vortex-like nature, the waves caused by the cilia being, even at this 

 spot, more or less felt ; and if, on the other hand, the particle be lifted by the wave of 

 the cilium into its superior part, the particle, passed on from one wave to another, will 

 make its way by fits and starts, but still, like those following the current in the middle 

 of the radial tube, without any contact with the flagellated cells. There are in the radial 

 tube two kinds of motions of the water, the rapid and direct current in the middle, and 

 the vortex-like near its walls, and both are unfit for the purpose of bringing the particles 

 in contact with the flagellated cells. Therefore, though not denying that the flagellated 

 cells may occasionally take in nutritious particles, I cannot admit that this is their 

 chief function — they have besides another task of a motor character. 



I find it, however, very doubtful whether the nutritive function must be ascribed, as Dr. v. 

 Lendenfeld does, to the ectodermic pavement-cells exclusively. He states that theflagella t e< 1 

 cells take in the particles of carmine in order to push them out forthwith ; lie states also 

 that the endodermic pavement-cells take in the particles of carmine too, but there is in the 

 paper no suggestion that these latter particles would be pushed out in their turn ; and if we 

 reflect upon the fact that (1), from the mechanical point of view, the ecto- and endodermic 

 pavement-cells are exactly under the same conditions, the water advancing calmly and 

 slowly along the outer surface of the sponge, and forming no whirlpools between the 

 gastric openings, these latter being of smaller diameters than those of the radial 

 tubes; that (2) mesodermic amoeboid cells, sparsely scattered near the flagellated 

 chambers, are quite as numerous near the layer of pavement-cells of the exhalent canal 

 system as near the subdermal cavities; that (3) the ecto- and endodermic pavement- 

 cells are histologically (at least in Calcarea) quite equivalent ; and that (4) there is no 

 room for the supposition that the nutritious particles having entered the sponge organism 

 could all be absorbed by the pavement-cells of the subdermal cavities ; if we reflect upon 

 all this, I think we must come to the conclusion that there are no reasons fur ascribing 

 different functions to the ectodermic and endodermic pavement-cells. 



