26 



C. M. CHILD. 



the differential thinning of the blastula wall and the direction of 

 locomotion of the larva all indicate a greater physiological activity 

 at the apical pole, the high end of the gradient, than elsewhere. 

 The question whether any gradient exists or arises in the en- 

 toderm is of interest, but the only method among those used which 





15 f6 



FIGS. 12-17. 



* 



is available for demonstrating the presence of such a gradient is 

 that indicating different amounts of reduction of permanganate 

 at different levels. After the entodermal cells have formed a defi- 

 nite internal layer in the planula the cleared permanganate prepara- 

 tions usually show a slight entodermal gradient in amount of 

 reduction, as indicated by depth of color. This gradient is similar 

 in direction to the ectodermal gradient but the differences at dill 



