230 



PROBLEMS OF RELATIVE GROWTH 



10- 



%10 



V 



p 



^ 2 



Extrusion 10 



20 30 



Time in Days , 



VO 



50 





Fig. 99. — Actual rate of darkening (smoothed curves) in 1,000 rapid-darkening 

 (n-SS) and 1,000 slow-darkening (rrss) specimens of Gammarus chevreuxi at 



23 C. (compare Fig. 98). 



mally small owing to the slow growth. Later, however, the 

 eye-colour is regulated towards what is ' normal ' for the 

 particular rate-genes involved; this appears due to the fact 

 that further formation of pigment occurs in relation to body- 

 size (Ford, 1928) ; Fig. ioo. 





12 



%> 



<^ 5 



I" 



v 

 * 



Time in Days 



Fig. 100. — Effect of size (rate of body-growth) on rate of eye-darkening in a 

 single genetic strain of Gammarus chevreuxi. 



All specimens were males of constitution rrss, kept at 23 C. The figures on the curves give eye- 

 length in mm. 



Max., curve of darkening in slow-growing specimens, which attain sexual maturity at time repre- 

 sented by vertical line C ; min., curve for fast-growing specimens (maturity attained at A) ; mean, 

 curve for mean of population (maturity attained at B). 



