10 



20 



30 10 



TUBE NUMBER 



Fig. 1. 



Sedimentation patterns of R-RNA extracted from ribosomes Isolated from 200 ^^ P- labeled: 

 a) unfertilized eggs, b) blastula embryos, c) gastrula embryos, d) neurula embryos, 

 e) hatching embryos, f) gill circulation embryos. Sibling embryos were used In this 

 experiment. 



embryos in the hope that it might yield some 

 clue as to the control of R-RNA synthesis. 

 Twenty -four hour (early gastrula) and forty- 

 eight hour (early neurula) 32p_iabeled control 

 and hybrid embryos were extracted for RNA 

 and the purified RNA preparation displayed on 

 a sucrose gradient (Fig. 2). All RNA prepara- 

 tions were treated with DNase prior to sucrose 

 density gradient analysis. It is evident from Fig. 

 2 that the hybrid embryos synthesize much 



less R-RNA at 48 hours than do the control 

 embryos. There is some question as to whether 

 the hybrid embryos synthesize R-RNA at all. 

 Stained histological sections of hybrid and con- 

 trol forth-eight hour embryos showed nucleoli 

 present in the control embryos but nucleoli 

 were not observed in the hybrids. The sucrose 

 density patterns, however, indicated that some 

 R-RNA was synthesized in the hybrid embryos. 

 Further work is necessary to resolve this point. 



36 



