[December 
148 Psyche 
of insects giving a positive reaction at a definite tempera- 
ture and humidity. 
Results 
The results of the foregoing tests are embodied in the fol- 
lowing graph (Fig. 2) . Neither at 20° C. nor at 40° C. was 
the percentage of response very high. The highest (57%) 
took place at 20° C. in a saturated atmosphere. At 30° C. 
there was a rise in percentage of response almost directly 
proportional to the increase in humidity, until the latter 
reached 73%, after which it fell slightly. At 30° C. and a 
Fig. 2. Olfactory responses of blow-flies. 
humidity of 73% the percent of response was 89; at a hu- 
midity of 100% it was 76. There was no indication of sex 
differences in these responses. The fact that there were 
practically no responses to the “check” indicates that it 
was really the vapor of ethyl butyrate and not air currents 
that brought about the responses. 
General Conclusions 
Several months of breeding and general observations in- 
dicate that the most favorable temperature for the meta- 
bolism of L. sericata is about 30° C. In the light of this 
fact, the discrepancies between the behavior of flies tested 
at that temperature and those tested at other temperature 
ranges can be easily understood. Apparently it is only at 
