THE GENETIC CONTROL OF PATTERN 



195 



the number of cells in mitosis). The mitotic rate is increased in those 

 areas which will later become darker, that is, the edges of the mid-field. 



Fig. 91. The Development of Wing Pattern in Ephestia. — At the left above (a) 

 is a diagram of the diffusion streams which lead to the formation of the midfield. 

 b to f show the results of wounds made in the first 24 hours of pupal life; the 

 streams have proceeded with their normal intensity, but have been checked by 

 the wounded spots. In g to / the wound was made later (24-72 hours) and the 

 streams have been halted at the point they had reached when the wound was 

 made, earliest in g and latest in /. An unoperated wing is shown in m. 



(From Kijhn.) 



The final effect involves not only the colour but also the shape of the 

 scales and the detailed distribution of pigment in them. 



Genes are known which affect the pattern of the wings in Ephestia 

 by altering the equilibrium pattern which is finally attained by the 

 determination stream. The dominant Sy (recessive lethal) causes the 



