2 DR. J. F. GEMMILL ON THE 



seemed of interest to investigate the ciliary activities of the 

 adult, especially as considerable attention has been paid of late to 

 the role of ciliation * in other animals, with results of much 

 importance alike as regards physiology and structure. 



Of the species available in the Firth of Clyde, Asterias 

 rubens L., Solaster papposus L., Porania pulvillus O. F. M-, and 

 Astropecten irregularis (Pennant), were selected for particular 

 examination, as belonging to families showing very great diver- 

 gence in form or larval history. 



In the course of the investigation, data were obtained indicating 

 that Porania secures a portion of its food-supply by ciliary 

 activity. This fact is of the greatest significance as showing 

 how nutritional continuity could have been maintained in the 

 progress of Asterid evolution, during the transition from a bi- 

 lateral, ciliary-feeding, pelagic ancestor, through an attached 

 stage allowing the gradual acquirement of radial symmetry, to 

 present-day starfishes which obtain their food-supply wholly or 

 mainly by capture through the agency of the sucker-feet. 



I. Ciliary Currents. 

 1 . Methods and Orientation. 



The direction of ciliary action on the different surfaces was 

 studied by pinning oat fresh living preparations from healthy 

 specimens, in sea-water with fine carmine particles in suspension, 

 and then examining under strong reflected light with the help 

 of a Swift-Stevenson binocular microscope. Occasionally, lamp- 

 black or dead Echinus sperm was used instead of carmine. In 

 the case of the ampullae and sucker-feet the corpuscles of the 

 water-vascular fluid served, under bright illumination, to demon- 

 strate the currents, but the results thus obtained were confirmed 

 by the use of carmine injections. 



As regards orientation, the specimens are to be considered as 

 lying on a horizontal surface with the abora] side uppermost. In 

 the text : — 



Superior, upwards, etc., refer to the aboral, and inferior, down- 

 wards, etc., to the oral aspect or direction. 



Centripetal means horizontally towards, and centrifugal horizon- 

 tally away from, the vertical or mouth-anal axis. 



Laterally inwards and laterally outwards indicate currents at 

 right angles to the vertical mid-radial plane of an arm. 



Perpendicular refers to currents rising directly from, i. e, per- 

 pendicular to, a surface or margin. 



Opposite currents starting along a line and passing directly out- 

 wards from it are described as shedding away from the line in 

 question. 



* Cf. Caelgben. O., Biol. Centralblatt, vol. xxv. 1905, pp. 308-322 (Actinians, 

 Madreporavians). Orton, J. H., Jour. Mar. Biol. Assn. U.K. vol. ix. 1912, pp. 444- 

 478 (Ascirlians, Molluscs); vol. x. 1913, pp. 19-49 {Amphioxus, Ascidians, Mol- 

 luscs) ; vol. x. 1914, pp. 283-311 (Bracliiopods, Polyclmetes, etc.). 



