3OO FERXANDUS PAYXK. 



through the tube and the percentage which failed to pass through 

 in one minute. 



This table shows that the average time of the flies bred in the 

 dark for sixty-nine generations (series no. i) is least, 13.9 seconds, 

 and the average of those bred only in the light (series no. 3) 

 is greatest, 17.62 seconds. This is a difference of 2.72 seconds 

 in favor of the flies bred in the dark. Likewise the percent- 

 age of flies which failed to pass through the lulu* in one minute 

 is less (25.1 per cent.) in series no. I than in series no. 3 (29.5 

 per cent.). Series nos. 2 and 4 were run as controls and the aver- 

 age time is intermediate between the two extremes, while the 

 percentage which failed to go through the tube is less than in 

 series nos. I and 3. However, I do not believe the difference 

 between any of the series great enough to be of any special sig- 

 nificance and the only conclusion which can be drawn is that the 

 darkness operating through a period of sixty-nine generations 

 has produced no visible effect in the reactions -of Drosopliila 

 to the light of a Welsbach burner. It should be pointed out, 

 however, that the only cave condition present in the experiment 

 is darkness; that it is possible and indeed probable that factors 

 other than darkness (constant temperature and moisture) may 

 play some part in the changes which have taken place in cave 

 animals. If this be true the real test comes not in rearing animals 

 in the darkness but in a true cave environment. 



That the constancy of the environment may be a potent factor 

 in the production of degeneration in cave animals is strengthened 

 by the recent unpublished experiments of Tower. In a letter, 

 August 2, 1911, Professor Tower makes the following state- 

 ment: 1 "It has been my experience that there is hardly any- 

 thing so injurious to breeding stock as a constant environment. 

 It will produce degeneration, reduced activity, and not infre- 

 quently will result in actual elimination of the race." Al-o 

 in the experiments of Calkins and others on pmto/o.i, it seems 

 that the constancy of the food supply and the consiuncx of the 

 chemical make up of the medium in which they lived, brought 

 about, at least a shorter cycle than occurs in a food Minnlv am! 



1 1 wish to thank Professor Tower for the permission to use tliN -Md-incnt before 

 it has appeared in print. 



