No. 459.] REACTIONS OF POMACE FLY. 161 
Table I. 
Distribution of five flies in a vertically placed glass cylinder after two 
minutes in darkness; the flies at the outset occupied the bottom section of 
the vessel, No. 6. 










en Numbers of trials. Totals. 
Without mechanical stimulation. 
I 2 3 4 5 
I I I 2 
2 I I 2 4 
3 I 2 3 
4 o 
5 3 I 3 7 
6 2 I a 3 E 
With mechanical stimulation. 
I 2 3 4 5 
I I I 2 3 4 
2 2 I I 2 
3 1 1 : 
4 1 : 
5 1 I : 
6 I 2 I 2 I 7 







Apparently, then, mechanical stimulation tends to induce the 
locomotion which results in this upward migration, or, in other 
words, it has a kinetic effect on the organisms. The direction 
of the movement indicates a negative response to gravity, a 
reaction which is more strikingly demonstrated in a succeeding 
experiment. The lesser degree of activity shown by the flies 
allowed to remain quietly in the darkness recalls the experiment 
of Loeb (’90) with plant lice, in which continued confinement in 
a dark chamber brought on a kind of “ dark rigor " (*Dunkel- 
starre’’). Jo 
Kinetic Effect of Light.— To test the possible kinetic influence 
of light the following experiment was tried. The glass cylinder, 
containing a single fly, was placed in a vertical position 1n the 
