672 HERRICK E. WILSON 



base, close the left-posterior and right-posterior sutures, and shift 

 the plates in accordance with Wachsmuth and Springer's theory. 

 We are here confronted at once with the fact that neither in Antedon, 

 in the live-basal hexagonal forms of monocyclic or dicyclic Crinoi- 

 dea. nor in the four-basal hexagonal Camerata. has any such 

 shifting taken place. Since the stimulus for widening the posterior 

 interradius has already accomplished its purpose, there is appar- 

 ently no stimulating cause to accomplish such a shifting, and if 

 there is no such stimulus, there is but one other alternative: the 

 phylogenetic succession as emended by Bather 1 and accepted by 

 Springer is artificial. 



Grant for the moment that the succession as outlined is artificial. 

 and starting with the ancestral form as proposed by Wachsmuth 

 and Springer, develop the hexagonal, equally tripartite base from 

 the pentagonal, unequally tripartite base. The anal plate being 

 inserted as proposed, let us follow closely the steps required in the 

 shifting of the basals. The posterior and left-posterior, the right- 

 posterior and right-anterior basals have already anchylosed in pairs, 

 which demands, as we have shown before, closed plate cycles. In 

 order that the right-anterior compound basal de may assume a 

 right-posterior position, as Wachsmuth and Springer have affirmed, 

 sufficient expansion must take place between the radials and the 

 basals to permit such shifting, or there must be absorption of the 

 distal angle of this basal, the proximal angles of the radials. or of 

 both coupled with inhibition of plate growth in order to permit 

 their passing. At the same time that widening in the anal area is 

 taking place there must be a compensating widening between the 

 two anterior basals. Tins change demands a movement of the 

 sarcode on the right side away from the anal plate in the radial 

 cycle and toward it in the basal cycle, winch is surely too remark- 

 able a tortion to be deemed possible, especially in forms having 

 the bilaterally symmetrical development shown in the camerate 

 Crinoidea. Furthermore, tins theory does not take into considera- 

 tion the fact that it is the stimulus arising from the push of the 

 rapidly developing intestine against the posterior interradius that 

 has caused the introduction of the anal plate. 



1 Ret. 6. pp 5 jo 2 Re;. 25, pp. 1. 



