INTERRELATIONSHIPS 69 



fig. I ) Simultaneously with the appearance of the anal plate, a slender digitate process 



rises from one side of the stomach and curves towards that plate; this constitutes the rudi- 

 ment of the Intestine. 



This is at a very early stage. At a more advanced stage, shown by figures 2, 

 3, Plate A, the account proceeds : 



The single anal plate originally interposed between two of the first radials (RR), being 

 attached not so much to the neighboring plates as to the visceral mass, begins to be lifted out 

 (as it were) from between them with the development 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 previ 

 ously interposed, but which do not yet come into mutual contact (p. 732). 



And further: 



The anal funnel (PI. A, fig. 2) 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. 



An important fact not stated by either of these authors, but which clearly 

 appears from Dr. Carpenter's figure (op. cit., pi. 41, fig. 1), is that the anal 

 plate does not abut upon the two radials equally, but has a closer relation to the 

 right posterior radial, whose margin is inwardly curved for its accommoda- 

 tion. In Sir Wyville Thomson's figure showing the position of the anal plate 

 and the caecal process from the stomach towards it (op. cit., pi. 27, fig. 1), the 

 plate is represented as closer to the left posterior radial, and the intestine as 

 curving to it from the left of the posterior interradius. This is contrary to all 

 other observations of this plate and of the intestine, and leads to the suspicion 

 that the figure may have been reversed in lithographing. 



The position of the anal plate in the same genus is also shown by Sars, 1 

 and its migration, as deduced from the works of the foregoing authors, is illus- 

 trated by Bather in the Lankester Zoology, p. 122, Figure xxx, in which he 

 has also shown the plate as abutting upon the radials by straight sutures, in- 

 stead of encroaching upon the one to the right by a curved margin. 



In later years Dr. Th. Mortensen, of Copenhagen, has made important 

 studies of the pentacrinoid stage of an Antedonid from Greenland, Hathro- 

 metra prolixa, in which the position of the anal at the left of the right posterior 

 radial is shown by an interesting series of figures. 2 As in Antedon bifida 

 (rosaceus auctt.), the plate is first observed after the radials and incipient 

 brachials have formed (op. cit., pi. 9, fig. 3). Mortensen's observations are of 

 particular value because his specimens were found in broods attached to the 

 cirri of the parents, and he had before him several developmental stages ; from 



1 Memoires pour servir a la connaissance des Crinoi'des Vivantes, 1868, pi. 5, fig. 3. 



2 Report Echinoderms collected by the Danmark-Expedition at Northeast Greenland, 19TO, p. 242; 

 pis. 9, figs. 1-5; 11, figs. 1, 5, 6; 12, fig. 5. 



