CILIATION OF ASTERIDS. 5 



with changing water, so that the respiratory function does not 

 completely cease. 



The ciliation on all attached or projecting parts (spines and 

 spinelets, pedicellaria?, sucker-feet, gills) is, on the whole, from 

 the attached to the free extremities, an arrangement promoting 

 the removal of debris. In Porania and Solaster, particularly in 

 the smaller-sized specimens, the skin on the aboral aspect between 

 the gills and spines is ciliated so as to collect particles towards the 

 anus, and throw them up therefrom in a perpendicular stream, 

 from under which the starfish is continually walking away in the 

 ordinary course of its movements. This somewhat remarkable 

 arrangement is illustrated for Porania in the accompanying 

 text-figure. In Asterias, the skin is too thickly covered with 

 gills, spines, and pedipellarise to exhibit such an arrangement of 

 currents, but the various structures named serve as the starting- 

 cones of minor ascending currents everywhere on the aboral 

 surface of the disc. 



The aboral ciliation of Astropecten follows entirely different 

 lines, and is possibly related to ciliary feeding (p. 14). The 

 ciliation on the oral aspect of Porania is of direct importance in 

 connection with the last-named function (p. 10). 



3 (a). Lining of Perivisceral Cavity : Somatopleure. 



Area. Description of Current. 



Floor of rays in middle line In Asterias centrifugal with irregularities ; in 



Solaster centripetal with irregularities ; in 

 Porania centripetal*; in Astropecten very 

 faintly centripetal *. 



Floor of rays close to either side Laterally inwards or outwards to or from 

 of middle line. middle line*; in Porania chiefly inwards ; 



in Astropecten chiefly outwards. 



Floor of rays over ampullaa of From base to summit of ampullae with centri- 

 sucker-feet. petal tendency, except in Astropecten where 



the tendency is centrifugal. 



Infero-lateral angles of rays Strongly centripetal, providing the chief oral- 

 ward streams. 



Buccal membrane Centripetal. 



Interbrachial septa Centripetal along inferior angles; centrifugal 



along superior angles ; mixed on sides ; 

 tendency * towards circular movement, over 

 the free edges of the septa, in a dextral or 

 watch-hand direction as viewed aborally. 



Aboral wall of ray (median Strongly centrifugal, 

 portion between the radial 

 caeca). 



Aboral wall of ray (portions Strongly centrifugal and slanting laterally 

 lateral to radial ca'ca). outwards, and then oral wards. 



Aboral wall of ray (portions Centripetal in Asterias and Porania , *; mixed 

 looking into the epigastric cue- in Solaster and Astropecten. 



lomic pockets). 



Lateral wall of ray Oralwards. 



* Currents somewhat variable. 



