MORPHOLOGY 59 



anal x in those genera being now filled by the greatly enlarged posterior basal, 

 which has risen to the level of the radials. In Taxocrinus intermedins, Plate 

 LIII, figures la, 2b, and T. nngula, Plate LV, figure 3, the plate is conspicuous 

 by its large size as compared with the succeeding tube-plates. In many exam- 

 ples of Forbesiocrinus, such as Plates XXVI, figure 5, and XXVIII, figures 4, 

 5, where the equivalent of the row of tube-plates is seen in the vertical series 

 of plates loosened at one side, the line of weakness which invited such a migra- 

 tion is clearly indicated. 1 If now we take the case of Protaxocrinus and 

 Gnorimocrinus, Plates XLVI, figure 8b and XLVII, figure 1, in which the 

 tube plates connect directly with the RA in the primitive and lower oblique 

 positions, we have the whole course of this migration marked by a plain trail. 

 We are now able to show, as will be pointed out further on, that the same 

 course of migration is followed by a corresponding plate during successive stages 

 of a Recent comatulid, that the trail thus indicated is that of the gut with which 

 the radianal in its earlier and progressive stages was closely associated, and that 

 the phylogenetic development of this character in a Paleozoic group is recapitu- 

 lated in the ontogeny of the living crinoid. The modifications of the anal inter- 

 radius as a whole, depending upon its occupation by solid plates or by a tube, are 

 considered under the next head. 



1 It is of interest to note that in the Camerata there is no such line of weakness — no sloping or leaning 

 to the right, even in the Reteocrinidae, which have a more or less flexible structure. 



