CILIATION OP ASTERIDS. 1 5 



escape through the mouth, as occurs in the feeding starfish-larva 

 (4, p. 240). However, I have not yet kept Astropecten alive for 

 long periods under the experimental conditions described above 

 in connection with Porania; and as regards the ciliation it must 

 be remembered that., in a burrowing starfish, general and local 

 respiration will best be promoted by currents drawn from the 

 aboral surface and the arm-tips. 



SoLASTER PAPPOSUS, and OTHER STARFISHES. 



S. papposus has powerful sucker-feet, the bi-serial setting of 

 which is more than compensated for by the increased number 

 of the rays. It feeds readily on almost any kind of animal food, 

 and in general the ciliation on the oral aspect, except in the ambu- 

 lacra! grooves, is away from the mouth. However, these grooves 

 are numerous : an oral ward current sets in strongly along each ; 

 active ingestion of carmine particles may occasionally be observed 

 to take place ; opening of the anus and expulsion of fluid occur 

 repeatedly * at certain times; carmine particles may be present 

 in the fluid expelled, if the specimen has been previously kept in 

 water with this substance in suspension ; and, finally, particles of 

 carmine may be found after death in the stomach of a similarly 

 treated specimen. Small Solasters kept under the experimental 

 conditions described in connection with Porania lose weight 

 and die off, but not so quickly as similarly-treated specimens of 

 Asterias rubens. On the whole, I should judge that while ciliary 

 feeding may, and probably does, occur to some slight extent in 

 the Solasters, it is a-sicle result of other processes which subserve 

 endodermal respiration and emptying of the food-canal. 



As regards other starfishes, I have had the opportunity of 

 investigating the ciliation on the oral surfaces of Asterias rubens, 

 A. glacialis, A. miilleri, Henricia sanguinolenta, Asterina gibbosa, 

 and Palmipes placenta. In none of these, however, are there 

 currents towards the mouth except along the ambulacra] grooves, 

 and, so far as my experiments have gone, none has approached 

 Porania in ability to survive after deprivation of solid food. 



Bearing on Phylogeny. 



It is generally agreed that the ancestor of Echinoderms was 

 a bilaterally-symmetrical ciliary-feeding pelagic organism, and 

 that radial symmetry was acquired during a stage of fixation. 



* In the tanks at the Millport Marine Station, where the Solasters feed freely, 

 the fluid expelled is dark green in colour, and is thrown out with considerable force. 

 In a particular specimen of large size, expulsions were observed to occur at intervals 

 averaging eight minutes during a period of an hour and a quarter, the arms remain- 

 ing open for from 4 to 6 seconds on each occasion. The first two or three expulsions 

 were powerful, the stream of coloured matter emitted into the water reaching a 

 length of nine inches. Ejection became weaker thereafter, and ceased at the end of 

 the period named. I am indebted for these data to Mr. R. Elmhirst, Superin- 

 tendent of the Millport Station, and to the Eev. W. Steven, B.A. 



