504 FRANK SPRINGER 



Between two of the radials, and at the same level with them, an unsym- 

 metrical plate early shows itself, the subsequent relation of which to the vent 



proves it to be an anal plate (Plate V, Fig. 4) Simultaneously with the 



appearance of the anal plate, a slender digitate process arises from one side of 

 the stomach, and curves toward that plate: this constitutes the rudiment of the 

 Intestine. 



This is at a very early stage. At a little more advanced stage, shown 

 by Figs. 5 and 6, Plate V, the account proceeds : 



The single anal plate originally interposed between two of the first radials 

 (R. R.), being attached not so much to the neighboring plates as to the visceral 

 mass, begins to be Hfted out (as it were) from between them with the develop- 

 ment of the anal funnel; and the space left by it is partly filled up by the lateral 

 extension of the two radials between which it was previously interposed, but 

 which do not yet come into complete contact (p. 732). 



At a still later stage: 



The anal funnel (Plate V, Fig. 6) is now a very conspicuous object, the anal 

 plate {x) which it bears on its outer side being altogether lifted out from between 

 the two first radials which it originally separated (p. 734). 



The anal plate finally disappears altogether before the adult stage is 

 reached, and the anus takes up its permanent position toward the 

 margin of the disk. 



Thus we see that the position and movements of the anal plate 

 are not governed by its connection with other plates of the aboral 

 side, but that they depend upon the shifting and development of the 

 gut, to which it is at an early stage attached. And we can readily 

 trace, in the movements of the plate thus indicated, striking analogies 

 to some of the anal conditions observed among the paleozoic genera. 



Now we have, in the two great living genera of the Flexibilia 

 Pinnata, just such differences in the position of the anus — though 

 in less degree — as we have supposed to occur among the ancient forms ; 

 viz., that of Antedon being excentric, while that of Actinometra, alone 

 of all known living Crinoids, is absolutely central. The excen- 

 tricity of Antedon, while producing an anal plate in the larval skele- 

 ton, is not sufficient, or sufficiently persistent, to affect the form of 

 the calyx in the adult, which in both genera has perfect pentamerous 

 symmetry. It may be, therefore, that we have in these living genera 

 a reminiscence of the long struggle among their paleozoic antecedents 

 between these opposing tendencies. 



