R. C. VON BORSTEL 195 



plete in certain genetic strains of the wasp Habrobracon and the 

 honey bee. 



3. Can the young embryonic system be regarded as a pool in 

 which mitosis freely occurs until blastulation, or do critical 

 periods exist during the cleavage stages? By observing develop- 

 ment taking place in punctured eggs and by irradiating and dam- 

 aging the nuclei of otherwise normal eggs, it was found that the 

 sixth or seventh cleavage is such a critical period in Habrobracon. 



4. What component of the cytoplasm is the agent of determi- 

 nate development? By studying the consequences of ultraviolet 

 irradiation of the egg cytoplasm, it appears that nucleic acid or 

 nucleoprotein, perhaps in a particulate system, contains the in- 

 formation necessary for determinate development in the insect 



egg. 



5. Is there any general method by which one can distinguish 

 between action of the nucleus and action of the cytoplasm in 

 bringing about an embryonic event? We suggest that photoreac- 

 tivation of ultraviolet radiation damage may be such a method. 

 When Habrobracon egg cytoplasm is irradiated, dose-reduction 

 by photoreactivation does not occur, but photoreactivation can 

 occur after irradiation of the nucleus. 



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Atwood, K. C, and A. Norman. 1949. On the interpretation of multihit 

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Bachem, A., and C. I. Reed. 1931. The penetration of light through 

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Bernheim, F., K. M. Wilbur, and C. B. Kenaston. 1952. The effect of 

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 Arch. Biochem. and Biophys., 38, 177-84. 



Blum, H. F., J. S. Cook, and G. M. Loos. 1954. A comparison of live 

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Bodenstein, D. 1955. Insects. In Analysis of Development, B. H. 



