FOSSILS OF THE BURLIXGTOX GBOUP. 333 



out of their way to avoid it, those coming from the posterior rays pass- 

 ing around on each side of it to the point of convergence of the others, 

 a little in advance of the opening. That the ambulacra! canals here, 

 under this point of convergence of the furrows in the under side of the 

 vault, always came together and connected with the upper end of the 

 convoluted frame work of the digestive sack, we can scarcely entertain 

 a doubt. 



Xow in looking at one of these specimens, especially an internal cast 

 of the vault, showing the furrows (or casts of them) starting from a 

 central, or nearly central point, and radiating and bifurcating so as to 

 send a 1.) ranch to each arm-base, while the opening or proboscis of the 

 vault (or the protuberance representing it in the cast) is seen to occupy 

 a position somewhere on a line between this central point from which 

 the furrows radiate and the posterior side, one can scarcely avoid being 

 struck with the fact that this point of convergence of the ambulacra, 

 under the vault, bears the same relations in position to the opening 

 of the vault, that the mouth of a Comatula does to its anal opening. 

 And when we remember that eminent authorities, who have dissected 

 specimens of the existing genus Comatula, maintain that these animals 

 subsisted on microscopic organisms floating in the sea water, such 

 as the Diatomaeea\ minute Entomostraca, etc..* which were conveyed 

 to the mouth along the anibulacral canals, perhaps by means of 

 cilia, we are led from analogy to think that the Palaeozoic Crinoids 

 subsisted upon similar food, conveyed in the same way to the en- 

 trance of the digestive sack. If so, where would there have been 

 any absolute necessity for a mouth or other opening directly through 

 the vault, when, as we know, the anibulacral canals were so highly 

 developed under it from the arm openings to the entrance into the 

 top of the alimentary canal ? Indeed, it seems at least probable 

 that if the soft ventral disc of Comatula had possessed the power 

 of secreting solid vault pieces, as in most types of Palaeozoic Crin- 

 oids, that these vault pieces would not only have covered over the 

 anibulacral furrows, as in the palaeozoic types, but that they would also 

 have hermetically covered over the mouth, and converted the little 



* BRONX mentions the fact (Klassen des Thierreichs. Actinozoa, II, p. 211,) that the remains of 

 Diatiimacece, of the genera yavicula, Actinocyclns Cotcinodixfiis. and of Entomostraea, were found 

 in the stomach of Conwtula. and suggests that when such objects in floating in the sea water came in 

 contact with the ambulacra! furrows or the pinnuls?. they were conveyed along these furrows to those 

 of the arms, and thence in the same way iuto the mouth. He ridicules the idea, sometimes suggested, 

 that the food may have been handed by the pinnulae or arms directly to the month. 



DTJARDIS ami HTPE also state < Hist. Xat. des Zoophytes Echind., p. 18, ) that the living Comatula 

 was ''nourished by microscopic Algae and floating corpuscles, which the vibratile cilia of the ambu- 

 lacra brought to the mouth." That they may have sometimes swallowed a larger object that acci- 

 dentally floated into the mouth, however, is not improbable, and would not, if such were the case, by 

 any means disprove the generally accepted opinion that these animals received their fooa almost en- 

 tirely through the agency of their ambulacral canal*. 



