PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 159 



THE CHICK EMBRYO 



Determinations of oxygen uptake by Shearer (1924) showed a higher 

 rate in anterior than in posterior parts; but in a later paper, without fur- 

 ther experiment, the earher data are discarded as without significance 



Fig. 54, A~G. — Differential reduction of Janus green in earlier stages of the chick embryo; 

 reduction indicated by stippling. A-C, progress of reduction in primitive-streaiv stage; D, E, 

 head-process stage; F, G, stage of first intersomitic groove; injury of neural folds and retarda- 

 tion of reduction indicated by small crosses (from Rulon, 1935). 



(Shearer, 1930). A recent study of dye reduction has given results of 

 value (Rulon, 1935). Reduction of Janus green to the red form by the 

 embryos occurs readily in low oxygen. In primitive-streak and head-proc- 

 ess stages rate of reduction decreases posteriorly from the region of the 

 node (Fig. 54, A-C) and the head process (Fig. 54, D) and laterally from 



