BASAL PLATES IN CRINOIDEA CAMERATA 553 



we must remember that we are not dealing with a completed model 

 in which the plates are of fixed and unchangeable size, and in which 

 every change of plate position must be accompanied by an entire 

 readjustment of the adjacent plates; we are dealing with a growing 

 organism in which there is a certain amount of flexibility in adjust- 

 ment by plate growth. 



If this theory for the interpolation of the anal plate is correct, 

 the first anal plates of Glyptocrinus, Platycrinus , and Dichocrinus 

 are homologous; and in further developing the theory for the 

 evolution of basal plates this view will be followed. 



[To be concluded] 



