NATURAL SCIENCES OF PHILADELPHIA. 87 



suggested an idea that had sometimes occurred to us, that probably tlie pore 

 pieces of the pseudo-ambulacral areas correspond to the recumbent arms in the 

 Cj'stoidea.* This certainly seems very probable, as it may be seen that the 

 ranges of these pieces merely lap, as it were, down the sides iqjon the lancet 

 pieces, and really form no part of the body, properly speaking. If this view is 

 correct, each of the ranges of pore pieces of each pseudo-ambulacral area must, 

 in the true Pentremites with wide lancet pieces, represent half an arm, the two 

 halves being, as it were, split apart by the wide lancet pieces coming to the 

 surface between. In Gr(jnatocri?ius, Nudeorinus, and some other groups with 

 merely linear lancet pieces, however, the two ranges of pore pieces meet along 

 the mesial furrow of each pseudo-ambulacrum, and alternately interlock, just 

 like the arm pieces in Actinocrinus, and other types in which the arms are com- 

 posed of double rows of pieces. If these suggestions are correct, the little 

 delicate free appendages often regarded as arms, would correspond to the pin- 

 nulai, sometimes called tentacles in descriptions of fossil Crinoids proper, and 

 Cystoids. The fact that these little appendages are themselves, at least in 

 some types, composed each of a double series of minute pieces, would be no 

 objection to this view, because this is exactly the structure of the piunulffi in 

 most of the Cystoidea with recumbent arms. The next question, then, would 

 be in regard to supplementary pore pieces. These, if the so-called pore piecesf 

 can be viewed as arm pieces, may be merely the first pieces of the pinnulae 

 modified to adapt them to the peculiar structure of the other parts. 



Supplementary Note to the foregoing remarks. 



A few days before receiving the proof-sheets of this paper from the printer, 

 we were provided, through the politeness of Mr. Billings, with an advance 

 copy of a very interesting and important paper of his on the Structure of the 

 Crinoidea, Cystoidea and Blastoidea, to appear in the July number of the Ameri- 

 can Journal of Science and Arts. We cannot state here in detail the various 

 points in which he agrees with or differs from us, but we will mention a few 

 of the latter. In the first place, he does not concur in a suggestion made by 

 us, in our paper read before the Academy in December, 1868, that certain facts 

 seemed to indicate that in the paleozoic Crinoids the ambulacral canals might 

 have been organized so that, in addition to their reproductive and other func- 

 tions, they could have conveyed microscopic objects through the arm-openings, 

 under the vault, to the digestive sack. He also thinks the convoluted internal 

 organ and canals radiating from the summit of the same to the arm-openings, 

 belong to the respiratoiy, and not to the digestive system. 



With respect to the first suggestion, we would merely state that we are not 

 disposed to insist upon it, as it was not stated by us as a demonstrated fact, 

 but we rather intended to state facts that seemed to us to point to that con- 

 clusion. We were led to do so, in part, by the statements of Bronn, and Du- 

 jardin and Hup^, that the food of the recent Crinoids was probably conveyed 

 along the ambulacral canals, by the action of cilia, to the mouth ; and partly 

 by the fact that in the palaeozoic types, there seems to be no opening what- 

 ever in the vault, at the point to which the ambulacra converge, and where, 

 from all analogy among recent Echinoderms, the mouth ought to be situated. 

 We are aware, however, that there are some strong and perhaps insuperable 

 objections to such a conclusion. And yet, there seems to be others of nearly 

 or quite as much weight, against the conclusion that the single opening seen 

 in the vault of these older Crinoids, always performed the double function of 

 mouth and vent. Amongst these may be mentioned the fact that this opening 



*Sinoe this was written we learn that Mr. Billings had arrived at the same conclusion 

 in regard to the corresponding pieces in Cadaster. 



t The t«rm pore pieces could not, of course, be applied to any of the pieces of the pseu- 

 do-ambulacra in the same sense that we would call tne ambulacral pieces of an Echinoid 

 pore pieces, because the pores in the Blastoids do not pierce these little pieces as tliey 

 do in the Echinoids, but merely pass in between them. 



1869.] 



