FIG. 11. Separation of the new oral rudiment from the old oral apparatus in the 

 fission of singlets and doublets. Silver preparations. 



A. Singlet. New oral rudiment shifted to position directly posterior to old oral 

 apparatus. 



B. Singlet. New oral rudiment posterior and to the right of old oral apparatus. 



C and D. Two focal levels of doublet animal. C. surface at upper focal level. D, 

 surface at lower focal level. Note that both oral meridians show nearly the same 

 stage as the one oral meridian of the singlet in B. 



Symbols for Fig. 11 are given in the legend for Fig. 12. 



189 



