26o 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



isolation from apical dominance and that under inhibiting conditions a 

 secondary isolation may occur nearer the apical pole than the primary 

 and determine a secondary invagination is suggested by Bellamy. These 

 modifications have been obtained with LiCl m/io, HgCU m/500,000, 



inv.2 



B 



inv.2 



znv. 



C D 



Fig. 105, .4 -D.— Differential inhibition in frog; gastrula stages. .1, equatorial gastrulation 

 and radially symmetrical embryo, LiCl m/ 10.6 2, 76 hr. from one-cell stage, water 20 hr.; 

 B, equatorial gastrulation and secondary invagination nearer apical pole, HgCL m/500,000, 24 

 hr. from one-cell stage, water 24 hr.; C, D, secondary invaginations, LiCl m/io, continuous 

 from one-cell stage, d.l., dorsal lip; hp., blastopore; y.p., yolk plug; inv. 2, secondary invagina- 

 tion (from Bellamy, 1919). 



o.ooi per cent formaldehyde, and KCN m/i,ooo with successive decreases 

 in concentration after 24 hours. 



Under experimental conditions permitting further progress of develop- 

 ment not only do the resulting forms represent various degrees of dif- 

 ferential inhibitions but with low concentrations or intensities unques- 

 tionable secondary modifications appear in later developmental stages. 



