W. S. VINCENT 19 



starfish oocyte is shown to be metaboHcally heterogeneous m 

 that a small fraction of the RNA possesses different solubility 

 characteristics and is metabolically very active; the rest of the 

 RNA is relatively inert according to these criteria. The correla- 

 tion between chromosomal, nucleolar, and cytoplasmic events, 

 particularly with respect to RNA, has led to a hypothesis of the 

 role of RNA and the nucleolus in the transfer of genetically de- 

 termined specificity to the cytoplasm. The RNA is considered to 

 be a carrier of structural specificity imparted by genetic loci, and 

 the nucleolus is suggested as a site of multiplication of these spe- 

 cific RNA molecules which are then transferred to the cytoplasm. 



Acknowledgment 



Gratitude is expressed for the help of Dr. Jean Brachet and mem- 

 bers of his staff in providing laboratory space and for many stimulat- 

 ing conversations at the Laboratory of Experimental Morphology, 

 University of Brussels, Belgium. The assistance of Dr. Maurice Errera 

 is also acknowledged in making the measurements for Fig. 3. 



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