THE NUCLEIC ACIDS 



nucleotides takes place. At the same time the amount of cytoplasmic proteins 

 increases. Their synthesis is apparently in some way linked with the nucleic acid 

 changes. 



This perinuclear region of high ultraviolet absorption has been 

 demonstrated for two types of cells in both of which it may be said that 

 the cytoplasm is highly absorbing, namely the sea-urchin oocyte 

 (Gaspersson and Schultz^^) (Figure 5), and the ovarian nurse cells 

 in Drosophila (Schultz^^). In the tgg of the toad (Painter and Tay- 

 LOR^^), there is a zone of cytoplasm next to the nucleus which stains 



2,S00 



Wavelength 



3,000 



Figure 5 Ultraviolet absorption spectra of different parts of an 



ovarian egg of the sea urchin, Psammechinus miliaris. From Gaspersson 



and ScHULTz'^ {By courtesy, Proc. Nat. Acad. Sci.). 



Strongly with pyronin. Gaspersson and Schultz themselves did not 

 observe such a perinuclear zone in root-tip cells of the spinach, nor 

 was it found by Ludford et alii^^ in their ultraviolet photomicrographs 

 of living malignant cells. 



Bracket ^^ has cited evidence from his embryological experience 

 which suggests that not always is there an immediate relationship in 

 development between nucleoli and cytoplasmic basophilia. In the 

 amphibian embryo, nucleoli are absent in early cleavage stages and are 



15 



