1876.] and Development o/Antedon rosaceus. 225 



It has further been shown that, besides the tentacular canal- system, 

 each arm and pinnule contains two canals, one superposed on the other, 

 communicating at the termination of the pinnules, and that while the 

 lower or coeliac canals open directly into the deeper portion of the coelom 

 or perivisceral cavity, the upper or suhtentacular, passing inwards as the 

 radial canals of the oral disk, become continuous with the upper part of 

 the " axial canal," which opens at its lower end into the deepest part of 

 the ccelom. Thus a complete continuity, alike central and peripheral, is 

 established throughout the whole of this space ; and the central canal 

 also receives what may be termed the " mesenteric sinuses " proceeding 

 from the plications of the internal wall of the alimentary cavity. Thus 

 it seems probable that the products of digestion, except such as may 

 transude directly 'through the double wall of the alimentary canal into 

 the ccelom. are collected into these mesenteric sinuses, and by them con- 

 veyed into the axial canal, and that from this centre the nutritive fluid 

 is circulated throughout the double system of canals, passing from one 

 to the other, centrally through the axial canal, and peripherally at the 

 extremities of the pinnules. I have distinctly seen a movement of 

 granular fluid in one of the canals of the arm of a Pentacrinoid, proceed- 

 ing from the extremity towards the centre ; and although I was unable 

 to distinguish with certainty in which of the canals it took place, my 

 impression is that it was the coeliac. If this be so, the suhtentacular 

 canals constitute the arterial or distributive, and the coeliac canals the 

 venous or collective, system. Now as the axial canal is bounded by a 

 columella strengthened by the piling-up of calcareous plates, its walls 

 can scarcely be supposed to have any contractile power ; whilst, on the 

 other hand, as the surface of the peritoneum lining the ccelom is ciliated 

 in other Echinoderms, it may be presumed to be so in Antedon : and thus 

 we may fairly surmise that the circulation is kept up by ciliary movement. 

 — If sea-water be admitted, as I believe it to be, through the ciliated 

 funnels of the oral perisome, into the cavity of the ccelom, the circu- 

 lating fluid will correspond in its mixed character to the " chylaqueous n 

 fluid of many aquatic Invertebrata. 



One important office of this circulation will obviously be to supply 

 nutritive material for the periodical development of the sexual apparatus ; 

 and no arrangement could be conceived more conducive to such a pur- 

 pose. For in the pinnules, whose turgidity indicates the enlargement of 

 the generative rachis into testes or ovaries (as the case may be), these 

 organs (as shown in figs. 8, 9) lie between the two thin-walled canals, 

 so that they can readily draw nutrient fluid alike from the going and from 

 the returning current. It can scarcely be doubted that the " chylaqueous" 

 fluid is aerated during its transmission through the canals of the arms and 

 pinnules, particularly as the clothing of very minute cilia which I have 

 detected on the dorsal side of the arms will serve to renew the stratum 

 of water in contact with them. 



r2 



