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PHYSIOLOGICAL GENETICS 



number of scales formed in the later dark areas is larger per unit 

 than in the light areas. A difference in the relative increase of the 

 number of scales in light and dark areas was not found. These 

 facts are in perfect harmony with Goldschmidt's discoveries (a 

 point not realized by the flour-moth investigators) ; t he occurrence 

 of many mitoses means that the cells in question have not yet 



(a) 



(b) 



CO 



Fig. 52. — Pattern of mitoses in young pupal wings of the flour moth, 66ft. a. 

 normal; b, shift toward the center in the mutant with narrow field of symmetry. 

 (From Braun, 1936, Arch. Entwicklgmcch. 135, Fig. 7.) 



reached the end of their multiplication period, after which 

 growth and differentiation (formation of scales) begins. They 

 are therefore retarded in differentiation as compared with the 

 cells that do not divide further. Another fact has been found by 

 Koehler which falls in line: in the flour moth the wing rudiment 

 folds up at a certain stage, and these folds coincide roughly with 

 the situation of the future zigzag bands. This, again, agrees with 

 Goldschmidt's observation, as the softer, less differentiated 

 parts of the pattern, located in the zigzag bands, which will still 

 undergo mitotic division, are the natural lines of folding. 



We spoke of different speed of differentiation of the scales in 

 the different areas of the pattern. This must not be mistaken 

 for different growth. This is roughly identical all over the wing. 



