GRAY CRESCENT MATERIAL IN FROG EGG. 259 



one half days after laying (until the tadpoles from the control 

 eggs had come out of the jelly) but though they developed surface 

 cilia and seemed to be composed of perfectly healthy tissue, they 

 never developed any semblance of a nervous system. 



I likewise destroyed the material in the region of the lower 

 hemisphere opposite the gray crescent in twelve eggs of the same 

 lot. Development proceeded beyond the blastula stage in only 

 six of these but from all six of them neurulas resulted. 



All of these experiments indicate that the material of the gray 

 crescent gives rise to the neural plate. 



PRINCETON, N. J., 

 April 15, 1918. 



