400 



C. M. CHILD. 



about them. The susceptibility gradient is the same with all 

 the reagents and methods of use noted in the preceding section 

 so that there can be. no doubt of the existence of an apico-basal 

 gradient which is fundamentally related to the activity ofjthe 



12 



living protoplasm. The more rapid progress of death down one 

 side of the blastula which is frequently observed is probably an 

 indication of differences in other axes, but on this point certainty 

 is impossible. 



,O 



14 



In the gastrula stage the same gradient appears (Figs. 16-18), 

 the apex of the gastrula, which represents the apical region of the 

 egg and blastula, being most susceptible, the basal least suscep- 

 tible. The susceptibility of the entoderm and the blastopore 

 region is very much lower than that of the other ectodermal 

 regions. The entoderm is still intact after practically the whole 

 ectoderm has disintegrated (Fig. 18) and in concentration's where 



