Figure 3. Developing striated muscle from a 25th day frog-embryo. A large 

 nucleus is shown in the stage of "collapse" after extruding some of its achromatic 

 material, which forms a clear zone immediately surrounding it. This clear 

 zone is in its turn shown by careful focussing of the section to be continuous 

 with a large pool of achromatic material above and to the right of the nucleus, 

 and a smaller pool below. Figure 4 is a key diagram to show these pools, 

 which have apparently been regarded by some observers as signs of degeneration 

 occurring in the developing muscle tissue. They appear, however, to be a 

 normal product of nuclear metabolism. X 1500. 



