J. R. GREGG 257 



eration of inorganic phosphorus from phosphoprotein, but other- 

 wise their significance in relation to hybrid developmental failure 

 is not clear, 



Deoxyribosenucleic Acid Synthesis 



It is plausible to suppose that hybrid embryos may fail to de- 

 velop properly because they cannot synthesize substances neces- 



IZine in- Hours 

 /OO 



HJQ 



50. 



1.0 



ControLs:h.r>iv. a O 



c^ 



■ 



8 9 10 II IH i5 16 n 18 



De-Yizlcypme'ntal Staae, of Controls ( Sfiumumij) 



Fig. 15. Deoxyribosenucleic acid in developing Rana pipiens and hy- 

 brid embryos. (From Gregg and L0vtrup, 1955.) 



sary for continued normal morphogenesis. Unfortunately, we 

 have practically no information about the synthetic capacities of 

 hybrid embryos of the type under consideration. The sole pub- 

 lished investigation of this question is that of Gregg and L0vtrup 

 (1955), who claim to have shown that deoxyribosenucleic acid 

 (DNA) is synthesized by hybrids at a normal rate until Stage 



