180 R- VENDRELY 



similar results in maturation and cleavage in the grasshopper. McMaster^^o 

 studied sea urchin cleavage and his results, in disagreement with those of 

 Pasteels and Lison on similar material are in agreement with the hypothesis 

 of the constancy of the DNA in nuclei. Elson et al}^-^ showed that the sea 

 urchin embryo reaches a normal diploid value per cell within a few hours 

 after fertilization, and this value remains unchanged thereafter. Marshak 

 and Marshaki22 using the method of isotope dilution (C"-labeled thymine) 

 determined the DNA content of Arhacia eggs to be 8.1 X 10"^ ng. (i.e. 

 8.1 pg.) per egg and 7.9 X 10-^ Mg (i-e. 7.9 pg.) per sperm. 



Microorganisms. Ogur et al}"^^ report the DNA content of the yeast cell 

 as 0.0062 pg., and Webb^^* gives for the average DNA phosphorus content 

 of the "unit cell" of Clostridium welchii (normal rod-shaped bacteria and 

 filamentous forms obtained by incubation in a magnesium-deficient peptone 

 medium) 0.00232 pg. DNA phosphorus (0.0245 pg. DNA). 



i2» R. McMaster, Anat. Record 113, 26 (1952). 



121 D. Elson, T. Gustafson, and E. Chargaff, J. Biol. Chem. 209, 285 (1954). 



i« A. Marshak and C. Marshak, Exptl. Cell Research 5, 288 (1953). 



1" M. Ogur, S. Minckler, and D. O. McClary, J. Bacterial. 66, 642 (1953). 



12* M. Webb, Science 118, 607 (1953). 



