258 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



According to Bellamy (1919), who has given particular attention to the 

 modifications of early stages, differential inhibition appears first in altera- 

 tion of the "cleavage ratio," that is, a graded decrease in rate of cleavage, 



d.L 



B 



C D 



Fig. 104, A-D. — Differential inhibition in early development of frog {Rana pipiens). A, 

 differential inhibition of cleavage, KCN m/ 1,000, 24 hr. from two-cell stage, then in KCN 

 m/5,000, 24 hr.; B, differential inhibition of dorsal lip in gastrulation, median region most 

 inhibited, LiCl m/10.62, 38 hr. from advanced cleavage; C, more extreme inhibition of gas- 

 trulation, median dorsal lip almost completely inhibited, lateral lips also retarded, LiCl 

 m/10.62, 28^ hr. from one-cell stage; D, equatorial gastrulation resulting from differential 

 inhibition, LiCl m/10.62, 76 hr. from one-cell stage (from Bellamy, 1919). 



greatest apically and decreasing basipetally. With certain degrees of this 

 inhibition blastomeres may be approximately the same size throughout 

 (Fig. 104, A). Under inhibiting conditions so severe that development 



1909; Doms, 1915; Baldwin, 1915, 1919; Bellamy, 1919, 1922; Leplat, 1920; Cotronei, 1921, 

 1922; Higgins and Sheard, 1926; Motomura, 1931; Holtfreter, 19346; Lehmann, 1933, 1936a, 

 b, 1937a, b, c, 1938. 



