410 THE HEREDITARY FACTORS AND DIFFERENTIATION 



Fig. 197 

 The action of rate-genes in determining eye-pigmentation in Garmnarus. 

 Ordinates, grades of colour between pure red (o) and black (14). Abscissae, time. 

 Above : smoothed curves for rapid-darkening {rrSS) and slow-darkening (rm) 

 red-eyed types (average of 1000 specimens for each curve) at standard temperature 

 (23° C). Below: variation of gene-expression due to temperature. All curves 

 refer to animals of the same pure stock (inbred rrSS). At 10° C, no melanin is 

 deposited, and the eye remains scarlet; at 13° C, melanin deposition only begins 

 at 20-24 weeks. The figure shows the facts over the range from 15° C. to 28° C. 

 M. sexual maturity. (From Huxley, Problems of Relative Grozoth, London, 1932 ; 

 after Ford and Huxley.) 



