362 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



St. 10 



St. 13 



st.l4 



st.12 



st.15 



c 150- 



Q- loo- 



se- 



O 



c ^ 



reactor 



<150- 



z 



cr 



'Too- 



50- 



stage: 10 11 12 13 



soluble fraction (= a) 



. 450n 



14 15 10 11 12 13 14 15 

 yolk fraction (=b),,,,, residual fraction (=c) 



=400- 



■350- 



300- 



nductor 



stage: 10 11 12 13 



14 15 



Fig. 36. Changes in protein and RNA content relatively to the DNA content during 

 gastrulation in Ranapipiens. A. The stages used, 10, 11, 12 in sagittal section, 13, 14, 15 in 

 transverse section; inductor stippled, reactor crosshatched. B, C, D, E, relative levels of 

 the protein nitrogen and RNA in the three fractions (see text) of the homogenised inductor 

 and reactor. F. Total relative levels of RNA in inductor and reactor. From Rounds and 



Flickinger, 1958 (modified). 



in (j) the dispersion of the tagged compounds around the labelled inductor and in 

 the induced structures, and (2) the incorporation of the chosen compounds 

 (radioactive glycine and adenine), in the host nuclei (Fig. 35). Several aspects 

 strongly suggest an active participation of the nuclei in the induction processes. 

 Some data obtained on chicken embryos favor the idea that the macro- 

 molecules responsible for the induction process include sulfhydril groups. The 

 distribution of such groups bound to proteins follows a characteristic sequence 



