74 H. E. EWING. 



begun in the forty-third generation, and at the end of the sixty- 

 third generation a total number of 239 adult, wingless individuals 

 had been obtained. In every instance the longest individual 

 was selected from among those of the same fraternity for carrying 

 on the subline. The results of these selections are given gra- 

 phically in Fig. 7, and in tabular form in Table VII. If we 

 examine the graph, or curve, in Fig. 7, we observe that there is a 

 great fluctuation of the heavy solid line which represents the 

 fluctuations of the means of the succeeding fraternities. The 

 highest mean is 1.882 mm., the mean obtained for the forty- 

 ninth fraternity and the lowest is 1.212 mm., the mean of the 

 fifty-eighth fraternity. The longest individual obtained was 

 1.99 mm. in length, the shortest obtained was 0.99 mm. in length, 

 or slightly less than one half that of the longest individual. 



Looking along the curve, or line which joins the different 

 fraternal means of these 20 generations, and disregarding the 

 fluctuations, w r e fail to find any general trend upward, and the 

 final mean obtained, 1.617 mm., is but little above the mean with 

 which we started, which was 1.525 mm.; and the next to the last 

 mean obtained, the one for the sixty-second generation, 1.527 

 mm., is within only two thousandths of a millimeter of the 

 original mean. We conclude, then, that selection had no effect 

 in shifting the mean of the line or strain, which is what Johannsen 

 would call the mean for the genotype. But why such great 

 variation in the means of the different fraternities? In the 

 forty-eighth generation and again in the fifty-eighth generation 

 we find a sudden and remarkable drop in the fraternal mean. 

 I observed that in both of these cases the laboratory became quite 

 cold, in fact so cold that it was very uncomfortable to stay in it 

 for any length of time. Hence at the time these means were 

 obtained I supposed that they were so unusually low on account 

 of the low temperature. Later I demonstrated experimentally 

 that a great change in temperature caused a correspondingly 

 great change in the size (hence length) of the individuals. 



