488 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



Hoiothuroidea 



Criniiidea 



Asterozoa 



Figure 17.— Dominant gradient patterns established by the hydrocoel, and subsequently 

 adopted by the other organ systems, in echinoderms. Early postmetamorphic stages lie 

 to the left, and succeeding stages in the named groups appear on the right. Above, 

 meridional gradients (Echinozoa). Below, radial gradients (Crinoidea and Asterozoa). 



