408 TEE AMERICAN NATURALIST [Vol. LV 



able distance apart, six class units or, to be more exact, 

 6.12 as stated in the first paragraph. In both low and 

 high selection lines it is to be noticed that the variability 

 has decreased and at the same time the mean values of 

 females and males have approached each other. This 

 approach is greater in the low than in the high line. 



Tables II and III give the sexual dimorphism for the 

 parental unselected generation and for each of the 42 

 generations of selection. Each table includes, for both 

 low and high lines, the value of the dimorphism for each 

 generation and the decrease since the beginning of selec- 

 tion. In the last column of each table there is a com- 

 parison of the dimorphisms in the two selection lines. 

 Table II includes only the offspring in the direct line. 

 Table III gives the data for the same series, but includes 

 sib matings as well as those in the direct line. 



Figures 1 and 2 show the decrease in graphic form. 

 The vertical scale is in factorial units as described above. 

 The upper horizontal line is at the level of the dimor- 

 phism value of the unselected population, which is 6.12 

 units in favor of the males. The lower horizontal line 

 indicates the position of zero difference between the 

 sexes. The scale at the left gives the actual dimorphism 

 values and the scale at the right the departures from the 

 original value. The continuous zigzag line gives the 

 values for each generation in the low selection series and 

 the dotted line those in the high selection series. Special 

 emphasis is to be laid on the fact that selection was not 

 for low or high sexual dimorphism, but for low or high 

 facet number regardless of dimorphism. In no sense can 

 it be considered as a direct selection for degree of 

 dimorphism. 



The result obtained when the offspring of all matings 

 are taken (Fig. 2) is not essentially different from that 

 obtained in the direct line. Since it gives the smoother 

 curve because of the larger number of individuals it will 

 be used as the basis of the following discussion. 



In the low selection line the dimorphism drops very 



