CILIATION OF ASTERIDS. 19 



PLATE II. 



Fig'. 3. Transverse section (diagrammatic) of arm of Asterias rubens L., showing 

 direction of ciliary currents on the various ectodermal, enterocoelic, and 

 endodermal surfaces, and also within the cavities of the sucker-feet and 

 ampullae. For the sake of simplicity, only one sucker-foot is shown on 

 either side of the middle line. Centripetal (p. 2) currents are marked 

 by dots and centrifugal currents by crosses. Ordinary arrows show cur- 

 rents running in the plane of the paper, that is, transversely to the axis 

 of the arms; while arrows with a dot on the shaft indicate that there 

 is in addition a centripetal tendency. Arrows enclosed in an ellipse 

 indicate currents flowing in the direction to which the arrow points, but 

 tending to take a spiral course. 

 4. Transverse section (diagrammatic) of arm of Porania, showing direction of 

 ciliary currents. The same general explanation applies, to this figure as 

 to fig. 3. 



Plate III. 



Fig. 5. Vertical section of Porania passing along one of the arms, and somewhat 

 obliquelj' across another arm to show body-wall after removal of stomach. 

 As in figs. 3 and 4 the arrows indicate currents approximately in the 

 plane of the paper, while the dots show centrifugal and the crosses centri- 

 petal currents. The tendency to dextral movement is indicated by the 

 curved arrows on the edge of the inter brachial septa (pp. 6, 9). 

 6. Vertical section (diagrammatic) through stomach etc. of Porania to show 

 direction ot ciliary currents on the endodermal and splanchnopleural 

 surfaces. At the actino-stomial margin the ring of buccal membrane 

 with outward ciliation should be noted. 



<>* 



