Revieivs — Wachsmuth 8f Springer'' s Monograph on CrinoicU. 37 



when they turn to the plate which they term x, the case is altered. 

 They start oif by saying that this "is the homologue of the ' special ' 

 or ' first ' anal plate of the Camerata, and rests upon the truncated 

 posterior basal." This begs the whole position : it is equivalent to an 

 assertion that x is suddenly developed in that position, and that it 

 cannot possibly be homologized with any plate that does not truncate 

 the posterior basal. As they express it on p. 132, "As the tube 

 became larger, the radials spread out [i.e. apart], and the vacant space 

 tlius formed was filled by a new plate x." This explanation, though, 

 involving a different, almost an opposing, principle, may possibly be 

 correct. But one would like to have some attempt at proof. One 

 would expect to be shown primitive genera in which x first 

 appeared as a narrow strip separating the radials and gradually 

 widening. But no evidence of the kind is adduced. As for the 

 argument based on a supposed homology with certain Camerata 

 (p. 130), it must be recognized clearly that the appearance of x 

 in Inadunata stands in no genetic relation to the appearance in 

 Camerata. If the plate x be not a primitive structure, then its 

 acquisition by Inadunata must have been independent of anything 

 that may have taken place in Camerata. The sole value of the 

 comparison lies in its suggestion that what was possible in one 

 group was also possible in the other. But among Inadunate 

 genera themselves, Carabocrinus has an obvious additional supple- 

 mentary plate in the anal area of the cup ; so that the possibility 

 of a similar origin for x may be freely admitted. The probability, 

 considering the persistence and frequency of the structure, is 

 a different matter.^ 



Before accepting the above hypothesis as to the origin of x, we 

 have to consider whether any other hypothesis has been proposed. 

 Wachsmuth and Springer do in fact honour with courteous and 



1 "Wachsmuth and Springer are "wrong in thinking that I ever denied the general 

 homology of x with any plate in the Camerata. In a passage, which they quote 

 almost accurately, I once said, " it may be pointed out that, as interradials do not 

 enter into the composition of the dorsal cup in any Fistulate, none of these 

 [anal] plates can wail be the homologues of interradials : in many of the Camerata 

 actual interradials are present in the anal area, but in the Fistulata at least we must 

 look elsewhere for the origin of the so-called ' anal' plates " {Ann. Mag. Nat.Sist. 

 [6], V, p. 319). Having regard to the meaning at that time attached to the term 

 ' interradials,' it is clear that this merely meant that the anals of Fistulata could not 

 have been developed by the modification of interradials, since no such elements pre- 

 existed in that suborder, whatever might have been the case in Camerata. As to the 

 coui'se of evolution in Ichthyocrinidse and the Camerata I said plainly (op. cit., p. 331) 

 " I can express no opinion." It shoidd have been impossible to infer from this that 

 " Bather makes no reference to the anal plates of the Ichthyocrinidae, but regards the 

 anals of the Camerata as morphologically distinct from those of the Fistulata 

 . . . . because they [Fistulata] possess no interbrachials." Again, I said 

 that one had no right to regard the anal plate of Antedon as a mere interradial 

 when there were no such plates in the other iuterradii. Wachsmuth and Springer 

 seem to think this nonsense (p. 139) ; yet in the very next paragraph they say that 

 the "large interradial plate " on which rests the anal tube of Thaumatocrinus " is not 

 a special anal, for a similar plate is interposed between the radials of the other four 

 sides." But this is the precise and legitimate converse of the very argument that 

 they ridicule. 



