CILIATION OF ASTERIDS. 



2. External Surface. 



Area. Description of Current. 



Bottom of ambulacra! grooves ... Centripetal in all; strongest in Porania and 



Astropecten, weakest in Asterias. 

 Margins of nmbulacral grooves on Laterally outwards in Asterias and Solaster ; 

 and between the bases of the laterally inwards and with marked centri- 



ambulacral spines. petal tendency in Porania; laterally inwards 



in Astropecten, especially in the grooves 

 between the groups of spines. 



Lateral aspect of rays On the whole aboralwards in Asterias and 



Solaster; perpendicular* at marginal edge 

 in Porania, and sometimes also in Solaster; 

 in Astropecten running strongly downwards, 

 i. e. towards oral aspect of the ray, in the 

 grooves between the large marginal plates. 



Aboral aspect of rays Shedding faintly away from mid-radial line in 



Asterias*; aboralwards with centripetal 

 tendency in Solaster and Porania ; in Astro- 

 pecten centrifugal along middle line and 

 slanting laterally outwards to either side. 



Interradial surfaces (oral aspect) . Centrifugal, i. e. away from mouth, in Asterias 



and Solaster; centripetal, i. e. towards 

 mouth, in Porania and Astropecten. Some- 

 times in young specimens of the former, and 

 usually in old specimens, there is a small 

 area near the oral angle of each interradius 

 with centrifugal ciliation. 



Interradial surfaces (lateral as- Aboralwards in Asterias and Solaster; oral- 

 pect). wards in Astropecten. 



Interradial surfaces (aboral as- Confused in Asterias; centripetal towards anus 

 P ec 't). in Solaster and Porania ; centrifugal in 



Astropecten. 



Actinal intermediate areas These areas are well marked only in Porania 



and there the ciliation is centripetal, i. e. 

 towards the mouth. 



Aboral aspect of disc Confused in Asterias ; centripetal towards ana 



opening in Porania; somewhat confused in 

 So/aster, but with slight centripetal tendency 

 towards anal opening; centrifugal in Astro 



Buccal membrane Entirely centripetal in Astropecten; centri- 

 petal except for narrow centrifugal zone at 

 martiin of mouth in Porania, as also in 

 Solaster, but with weaker centripetal ciliation 

 in the latter; centrifugal all over in 

 Asterias. 



Madreporite Centrifugal in Astropecten; from periphery 



towards centre of madreporic surface iii 

 Asterias and contrariwise in Solaster and 

 Porania. 



Gills From base to summit somewhat spirally. 



Spines From attached to free ends often spirally. The 



large spines (denticles) projecting oral wards 

 from the interradial angles of Solaster are 

 ciliated towards the base on the lower, and 

 towards the apex on the upper aspect. In 



* Currents somewhat variable. 



