CILIATION OF ASTEItlES. 1 1 



particles, I found that there were periods during which extremely 

 active ingestion of the particles through the mouth into the 

 stomach occurred. The following structural or functional peculi- 

 arities in Porania next claimed attention. Taken as a complex 

 they seem direct adaptations for ciliary nutrition : — 



1. The cilia all over the actinal surface (in ambulacral grooves, 

 round bases of spines bordering these grooves, on actinal inter- 

 mediate areas, on buccal membrane, and on denticles) act in such 

 a way that streams of particles are continually converging on the 

 mouth-opening. 



2. The general shape of the starfish with its large flat inter- 

 mediate areas, ensures that there is an extensive circumoral 

 ciliated field, adapted for food-gathering purposes. 



3. The endodermal ciliation sweeps particles which have entered 

 the mouth into the recesses of the digestive system. We note, in 

 this connection, the aboralward ciliation of the pharyngeal and 

 radial stomachal legions, the centrifugal ciliation of the floor- 

 grooves of the radial caeca, the centripetal ciliation of the roof- 

 grooves of these caeca and of the radial grooves in the roof of the 

 pyloric sac, the aboralward ciliation of the intestine, and the 

 centrifugal ciliation within the interradial caeca. 



4. Every specimen of Porania that I have watched long enough 

 has shown periods, sometimes lasting several hours, during which 

 at sub-regular intervals the anus opens and a considerable 

 quantity of clear fluid (two to four grammes) is forcibly expelled 

 therefrom. In a particular specimen this occurred, on an average, 

 at intervals of eleven, in another of twenty-five, and in another 

 of forty minutes. Simultaneous observation by means of a 

 suitably adjusted microscope showed that shortly after each 

 expulsion of water from the anus there began a period of active 

 ingestion of carmine particles by the mouth and that this period 

 ceased just prior to the next expulsion. 



5. Mucus is secreted by the epiderm of the oral surface and 

 also by the gastric endoclerm. To judge by what happens with 

 carmine particles, this mucus is capable of entangling small 

 food-particles, and of so causing the formation of rafts or ropes 

 of nutritive material which travel slowly into the recesses of the 

 digestive cavity. 



6. On killing a specimen which had lived for some time in 

 water with an admixture of carmine particles and had exhibited 

 the phenomena described under 5 above, I found carmine particles 

 in the gastric cavity and in the radial caeca. Again, in the cate 

 of living specimens which had been "fed " on carmine, abundance 

 of the particles appeared in the fluid expelled from time to time 

 by the anus. In preparations of the living tissues one can 

 demonstrate the readiness with which particles are swept intt, 

 and out of the radial caeca, collected round the entrance to the 

 intestine, and even (though this occurs less easily) carried along 

 the intestine into the rectal caeca. 



7. The interradial or rectal caeca of Porania are exceptionally 



