482 Mr. F. A. Bather on some 



anal plates and adjoining radial, had a common origin in all 

 these genera, and were gradually evolved from a simple 

 azygous plate." 



Conclusion, (a) Wachsmuth and Springer think that an 

 azygos plate existed in the dorsal cup of the Fistulata (to 

 which group the context shows they are referring) before 

 either the special anal [x] or tiie riglit posterior radial. 



(/3) Wachsmuth and Springer think that from this azygos 

 plate both the special anal [^x] and the riglit posterior radial 

 were derived. 



But is this azygos plate homologous with the azygos 

 plate o^ Dendrocrinus and the Cyathocrinidse generally? 



P. 375. Figures 1, 2, 3, 4, 5, 6, 8, 9, representing " the 

 arrangement of the plates of the azygous side in " Baero- 

 crinuSj Hoplocrinus^ Hyhocrinus, locrinusj Dendrocrinus, 

 Homocrinus^ Poteriocrinus^ and Eupachycrinus. In each of 

 these occurs a plate marked a. " a, azygous plate." 



Conclusion. Wachsmuth and Springer consider that the 

 azygos plate of Baerocrinus is homologous with that of other 

 Fistulata. 



P. 374, last par., continued on p. 375. This paragraph, 

 which is really too long to quote in full, explains how the 

 " large undivided azygous plate " oi Baerocrinus " was gradu- 

 ally absorbed by the radial," i. e. right posterior radial, which 

 in Baerocrinus itself " is not developed." This produces 

 Ho'plocrinus. In Hyhocrinus the radial " has absorbed a 

 greater portion," and " the upper left corner of the azygous 

 plate has become divided off into a special anal plate." 



Conclusion, (a) The azygos plate of Baerocrinus is the 

 " simple azygous plate " of p. 368, from which the special 

 anal aud the right posterior radial were gradually evolved. 



[Ip) Wachsmuth and Springer take Baerocrinus as the 

 ancestral form, primitivfi in regard to its posterior side. 



Summary of Wachsmuth and Sj^rinyer^s views. — There is in 

 the Fistulata a plate not radial in origin, azygos in position, 

 more conspicuous in the earlier forms ; a plate that exists 

 when even the radials are not fully developed, and from 

 which another anal plate and a radial are evolved. So far 

 then as the Fistulata are concerned this " azygos " plate is 

 a primitive, independent morphological element of the dorsal 



cup. 



This is the rational conclusion of a perfectly consistent 

 hypothesis. But it is a conclusion which, when pointed out, 

 does more than anything else to show the worthlessness of 

 the assumptions on which it is based. Messrs. Wachsmuth 

 and Springer are now as much astonished at it as I was, and 



