8 DR. J. F. GEMMILL OX THE 



groove on the roof of the pyloric sac. The circulation within 

 the pyloric caeca seems to depend entirely on ciliary action, 

 contractions of the walls of the caeca either not occurring or 

 being exceedingly slight and irregular. 



As regards the rectal caeca, all the ciliary currents appear to 

 be centrifugal, that is, outwards into the lobules. The return 

 currents from the caeca must therefore be passive so far as 

 ciliation is concerned. However, as is indicated below (p. 12), 

 the rectal caeca of Porania show rhythmic contractility, while 

 those of Solaster and Asterias, and probably of other starfishes, 

 are also contractile. The rectal caeca may therefore be emptied 

 or the fluid within them kept from stagnation by the muscular 

 action of their walls. 



5. Minor Cavities. 



Area. Description of Current. 



Dorsal sac Definitely, but not strongly ciliated. In a 



particular case (Solaster papposus) the 

 c irrent passed sinistrally across the roof, 

 and dextrally* across the floor of the sac. 



Axial sinus (general lining) On the whole aboralwards, and therefore tending 



to sweep particles towards the madreporite 

 (see 4, p. 246). 



Pore-canal system of madreporite . Weakly aboralwards. 



Interior of stone-canal Strongly oralwards (see 4, p. 269). 



Surface of stone-canal looking into Somewhat indefinite, strongest on the grooves 

 axial sinus. between the calcareous plates of the canal- 



wall, and following the lines of these grooves, 

 but on the whole with an aboral tendency. 



Periluemal spaces (aboral, oral, Ciliation feeble, flickering, strongest on surface 

 circular, and radial sinuses). of htemal tissue ; no definite direction of 



resulting currents noted. 



Lining of sucker-feet Upwards into arm along inner side, i.e., side 



nearest middle line of arm ; downwards to- 

 wards sucker along outer side, i. e., side 

 furthest away from middle line of arm. 

 Similar currents are found within the am- 

 pulls, i. e., upwards on inner aspect of am- 

 pullary wall, laterally outwards within dome 

 of ampulla, and .downwards towards sucker 

 on outer wall of ampulla. 



Peribranchiitl spaces and spaces of No ciliary activity made out. 

 body- wall. 



General. — The aboralward ciliation of the lining of the axial 

 sinus is of importance, since by its means particles may be swept 

 from the axial sinus into the stone-canal or the pore-canals (see 

 4, p. 270). The fact that the perihaemal spaces are ciliated does 

 not seem to have been previously ascertained. The absence of 

 ciliation from the lining of the peribranchial spaces is a point of 

 considerable interest. 



* Clockwise as viewed aborally. 



