CILIARY ACTION IN PLEUROBRACHIA PILEUS. 



263 



17 Ciliary Action in the Internal Cavities of" the Otenophore 

 Pleurobrachia pileus Fabr. Bv James F. Gemmill, 

 M.A., M.D., D.Sc, F.Z.S. 



[Received October 2, 1918 : Read November 5, 1918.] 

 (Text-figures 1 & 2.) 



During life ciliation is active throughout the internal cavities 

 of Pleurobrachia ; and the latter are wide enough to allow the 

 direction of the ciliary action on their different surfaces to be 

 made out from the motion of particles suspended in the con- 

 tained fluid, e. g. small oil globules, alimentary particles, and 

 debris. 



The "circulation" * is an extremely orderly one and meets the 

 physiological need for continuous regulated change through the 

 whole of the internal cavities. 



On the whole the circulation inside the funnel system goes 

 on independently of that within the stomodaaum f. So far as I 

 could make out, except under the influence of peristaltic action, 

 only slight interchange of fluid between the stomodaaum and the 

 funnel takes place. 



T. Stomodceum (text-figs. 1 & 2). 



Round the margin of the mouth there is a very narrow band 

 best seen in young specimens, the cilia of which strike into 

 the mouth-cavity. Up the middle of each lateral wall of the 

 stomodaaum, and continued on the thickenings in this region, and 

 to the infundibular opening, there is a track with aboralward 

 ciliation. Over the rest of the lateral wall of the stomodaaum the 

 ciliation is oralvvards with a slant towards the sagittal angles. 

 Along the sagittal angles from the opening of the funnel to that 

 of the mouth the ciliation is stronger and in the oralward 

 direction. 



II. Funnel and Canal System (text-fig. 2). 



We may best follow the circulation here by beginning in the 

 floor (oral wall) of the funnel at points on opposits sides of the 

 opening from stomodaeum into funnel. It will be remembered 

 that the aboralward currents up the middle of the sides of the 

 stomodaaum lead to these points. Working transversely outwards 



* Reference may be made to the following recent papers on ciliation : — 



Carlgren, 0. Biol. Centralbl. xxv. 1905, pp. 308-322 (Actinians, Madreporarians). 

 Orton, J. H. Jonrn. Mar. Biol. Assoc. U. K. ix. 1912, pp. 144-478 (Ascidians, 

 Molluscs). 



Orton, J. H. Ibid. x. 1913, pp. 19-49 (Amphioxus, Ascidians, Molluscs). 

 Gemmill, J. F. Proc. Zool. Soc. Lond. 1915, pp. 1-19 (Starfish). 

 Widmark, E. M. P. Zs. Allg. Phys. Jena, xv. 1913, pp. 33-48 {Aurelia aurita). 

 f In this paper the whole of tbe cavity between mouth and funnel-opening is 

 called stomodseum. 



19* . 



