136 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



The change in condition of the basal region preceding gastrulation, as 

 indicated by dye reduction, suggests that it is undergoing activation; the 

 changes in its developmental behavior — immigration of the mesenchyme, 

 invagination of the entoderm — also suggest that a change of some sort has 



Fig. 47. — Differential dye reduction in late blastulae of Patiria; reduction more rapid on 

 one side, the left in the figure, presumably the ventral side (from Child, 19360). 



A 



B 



Fig. 48, .4, B. — Differential susceptibility of late Strongylocentrotus blastulae to lack of 

 oxygen and to cyanide. A, before immigration of mesenchyme only mesenchyme cytolyzed 

 in basal region; B, after immigration mesenchyme and middle entodermal region cytolyzed; 

 ventral(?) side more susceptible than dorsal (from Child, 1936a). 



occurred. If the change is an activation, as dye reduction suggests, it is 

 not necessary to assume that the two opposed gradient systems represent 

 identical activities. Gradients involving different metabolic reactions and 

 different protoplasmic substances may be similarly indicated by reduction 

 or susceptibility differentials. 



