ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 373 



The direction of ciliary action on the different surfaces was studied 

 by pinning out fresh living preparations from healthy specimens, in sea- 

 water with fine carmine particles in suspension, and then examining 

 under strong reflected light with the help of a Swift-Stevenson binocular 

 Microscope. Occasionally, lamp-black or dead sperm of the sea-urchin 

 was used instead of carmine. In the case of the ampullae and Bucker- 

 feet the corpuscles of the water-vascular fluid served, under bright 

 illumination, to demonstrate the currents, but the results thus obtained 

 were confirmed by the use of carmine injections 



There can be little doubt that all over the surface of the body the 

 ciliary currents subserve local respiratory purposes, a function of much 

 importance in connexion with the great superficial nerve-tracts, inas- 

 much as these tracts cannot readily receive adequate oxygenation from 

 the perihaernal fluid bathing their deep surfaces. The currents along 

 the ambulacral grooves are centripetal ; fresh water is thus always being- 

 brought along them towards the nerve-ring and centre of the disk. 

 This may lie important during periods when the starfish is stationary, 

 as in feeding, or is wholly or partly buried in sand (Astropecten). 

 Palpules are sometimes introverted (Porania), and as the spiral ciliation 

 of their epidermal surface keeps this surface bathed with changing 

 water, the respiratory function will not completely cease. 



The ciliation on projecting parts is, on the whole, from the attached 

 to the free extremities, thus promoting the removal of the debris. In 

 Porania and Solaster, particularly in the smaller specimens, the skin on 

 the aboral aspect between the gills and spines is ciliated so as to collect 

 particles towards the anus, and throw them up therefrom in a perpen- 

 dicular stream, from under which the starfish is continually walking 

 away in the ordinary course of its movements. In Asterias the skin is 

 too thickly covered with gills, spines, and pedicellarire to exhibit such 

 an arrangement of currents, but the various structures named serve as 

 the starting-cones of minor ascending currents everywhere on the aboral 

 surface of the disk. 



The lining of the perivisceral cavity is richly ciliated, and the 

 ciliation produces constant and complete mixing of the ccelomic fluid 

 in the interior of the disk and arms. Great centripetal currents flow 

 along the infero-lateral angles of the arms and, reaching the splanchno- 

 pleure of the gut-wall, are swept aboralwards and are next driven 

 centrifugally outwards towards the arm-tips by the cilia on the aboral 

 body-wall and on the radial and rectal cajca. There appears to be a 

 certain amount of circular movement on the part of the ccelomic fluid 

 in the dextral or watch-hand direction as viewed aborally. Continual 

 changing of the fluid inside the gills also occurs. 



The endoderm lining of the gut is also ciliated, and the major result 

 of this is to effect sweeping from mouth to anus, but we have also to 

 recognize certain secondary results ensuring : (a) mixing and delay 

 within the. main gastric cavity, and (b) circulation within the esecal 

 outgrowths. 



The aboralward ciliation of the lining of the axial sinus is also of 

 importance, since by its means particles may be swept from the axial 

 sinus into the stone-canal or the pore-canals. The fact that the 



Aug. 18th, 1915 2 D 



