CILIATION OF ASTEUIDS. 7 



Area. Description of Current. 



Stomachal portion of gastric cavity. Chiefly aboral wards, and strongest along the 



major radial furrows, but many of the inter- 

 radial furrows and some of the minor radial 

 furrows show oralward ciliation. 



Circular groove between stomachal Slight tendency to circular movement* in a 

 and pyloric-sac portions of sinistral direction as viewed aborally. 



gastric cavity. 



Pyloric sac, radial grooves Strongly aboralward or centripetal, i.e., to- 

 wards the intestinal opening near centre of 

 roof of sac. Note that in Solaster each of 

 these grooves (probably through secondary 

 sealing of its edges) forms a canal which 

 opens centrally near the commencement of 

 the intestine, and peripherally near the place 

 of origin of a pair of radial caeca. 



Pyloric sac, interradial areas Diffusely centrifugal, i. e., away from intestinal 



opening. 



Pyloric sac, rosette of minor Centripetal, i. e., towards entrance to intestine, 

 grooves round opening of in- 

 testine. 



Stalks of pyloric caeca Entrance to each pair of caeca is centripetally 



ciliated all round *. 



Roof-grooves of pyloric caeca Strongly centripetal. 



Floor-grooves of pyloric casca Strongly centrifugal. 



Folded sides of pyloric caeca Aboral wards, i.e., from floor-groove to roof- 

 groove. 



Intestine From pyloric sac towards rectal sac. 



Rectal caeca Centrifugal, i. e., into recesses of caaca. 



Rectum Not ascertained. 



General. — The major result of the endodermal ciliation is to 

 effect sweeping from mouth to anus, but we have also to recognise 

 certain secondary results ensuring : (a) mixing and delay within 

 the main gastric cavity, and (b) circulation within the csecal out- 

 growths. As factors under (a), note the oralward ciliation of 

 many of the folds and grooves in the stomachal portion of the 

 gastric cavity,, the oralward ciliation of the large interradial areas 

 in the roof of the pyloric sac, and the circular movement (clock- 

 wise as viewed from the oral aspect) recognisable near the groove 

 separating the stomachal and pyloric-sac portions of the gastric 

 cavity. The aboralward ciliation of the pharyngeal portion of 

 the gastric cavity will prevent particles from passing out of the 

 gastric cavity during the mixing process. As regards the radial 

 caeca, experiment shows that carmine grains are swept with great 

 rapidity centrifugally outwards from the gastric cavity along 

 their floor-grooves, the streams getting gradually smaller as the 

 apices are nearecl, since numerous small side-currents pass aboral - 

 wards along the walls of the caecal folds. The last-named 

 currents join the great centripetal stream which passes along the 

 roof -groove of the caecum and then along the corresponding radial 



* Currents somewhat variable. 



