4 DR. J. F. GEMMILL ON THE 



Area. Description of Current. 



Porania and Astropecten the entire ciliation 

 on these spines is from base towards apex. 

 As a rule, gills and spines set on any surface 

 which causes a definite current are ciliated 

 so as to promote this current for some dis- 

 tance up from their bases. 



Sucker-feet Prom attached to free ends spirally, but showing: 



irregularities in Asterias ; ciliation absent or 

 extremely weak in Solaster, Forania, and 

 Astropecten. 



Pedicellariae Irregular, but, on the whole, from attached to 



free ends. 



Paxillary spinelets of Astropecten. Weak from base to apex. 



General. — There can be little doubt but that all over the surface 

 of the body the ciliary currents subserve local respiratory purposes, 

 a function of much importance in connection with the great 

 superficial nerve-tracts, inasmuch as these tracts cannot readily 

 receive adequate oxygenation from the perihaamal fluid bathing 

 their deep surfaces. 



Since the currents along the ambulacra! grooves are centripetal 

 (p. 2) fresh water is always being brought along them towards 

 the nerve-ring and centre of the disc. This circumstance may 

 well be of importance during periods when the starfish is 

 stationary, as in feeding, or is wholly or partly buried in sand 

 [Astropecten). 



Text-figure 1. 



Diagram illustrating the arrangement of the aboral ciliary currents in Porania. 

 An., anus ; Madr., madreporite. 



We may note that occasionally a number of the papules, in- 

 stead of showing the usual everted or protruding condition, are 

 found to be introverted (Poranta). At such times, the spiral 

 ciliation of their epidermal surface keeps this surface bathed 



