Modification of Germinal Constitution of Organisms i6i 



By this means the color changes induced by these experiments were 

 known to be purely somatic modifications. Moreover, a control series, 

 derived from the same parents, was kept under normal conditions as a 

 check. During the series also several lots were taken from the e.xperi- 

 ments and placed for several generations in normal conditions, and were 

 then returned to experiment; and likewise lots were taken from the 

 control and placed in experiment; and subsequently returned to con- 

 trol. In this way a complete check was kept on the experiments. In 

 Fig. 60 are represented the generations experimented ui)on and the 

 proceedings followed with each. 



The experiment was divided into two parts — the experiment proper 

 (27a) and the control (276). In 27a the beetles were subjected to the 

 conditions of e.xperiment during ten lineal generations, with results 

 shown in Fig. 61. A maximum deviation in coloration was produced 

 at once toward a melanic state from which there was no deviation either 

 above or below in the succeeding generations. In the third genera- 

 tion of 27a the progeny were divided into two lots of equal size, one of 

 which was kept in the conditions of experimentation, and the other 

 returned to natural conditions. This second lot, known as 27a', after 

 being bred during four generations in normal surroundings, was further 

 separated into two portions, one of which was still kept in normal con- 

 ditions as 27a"', while the other was returned to the conditions of 

 experimentation as 270'*^. When the beetles in 27a' were returned to 

 normal surroundings, they at once resumed their natural characters 

 and did not deviate therefrom during the four generations of 27a and 

 the three of 27^'^, or seven in all. However, the efifect upon 270''^ of 

 being returned to the conditions of experiment was an immediate 

 return to the maximum melanic tendency before observed. From 

 the sixth generation in 27a another lot of beetles, 270^ were taken 

 and reared in normal conditions, with the result that they also immedi- 

 ately reverted to the parental condition, and the same was true of 270^ 

 in the ninth generation. In experiment 276 there appears a slight 

 oscillating variability which, however, is of no consequence. In the 

 second generation 276 was likewise separated into two lots of equal 

 size, one of which, 276, was retained as control, while the other, 276", 

 was placed in the conditions of experimentation for four generations, 

 and later in the seventh generation returned to control with 276. 



