THE OLFACTORY SENSE OF COLEOPTERA. 427 



The apices and bases of these cases rested on two supports above 

 a rigid table near a window. No screen was used to prevent 

 the beetles from seeing the observer because they never showed 

 any responses to the movements made by the observer. 



The following sources of odors were used for determining the 

 reactions of the beetles in the experimental cases; chemically 

 pure essential oils of peppermint, thyme, and wintergreen; parts 

 of plants — leaves and stems of pennyroyal {Hedoma pulegi- 

 oides?), and of spearmint {Mentha spicata); decayed matter 

 —parts of decayed beetles {Harpalus pennsylvanica) . All 

 these substances were kept in stoppered vials of the same shape 

 and size. The leaves and stems of the pennyroyal were dried, 

 but they still gave ofT a strong odor when the vial was uncorked. 

 The leaves and stems of the spearmint were fresh and they did 

 not emit as strong an odor as did the other substances used. 

 Beetles were killed and were torn to pieces. The pieces were put 

 into a vial and after two or three days they emitted a foul and 

 sickly odor. 



A beetle was carefully placed into one of the experimental 

 cases. When first put into the case the insect usually wandered 

 about for several minutes, but finally it became quiet. The 

 insect was tested with the above odors only when it had become 

 perfectly quiet, without the antennae being moved in the least. 

 The stopper of a vial was quickly removed and the vial was gently 

 and slowly placed under the experimental case directly beneath 

 and within one half inch of the individual being tested. When 

 all of these precautions are taken, a normal beetle generally 

 responds to anyone of these odors within 60 seconds, but when 

 all the reaction times are counted, it is seen that several of them 

 failed to respond within 60 seconds. If a beetle when tested fails 

 to react to an odor within 60 seconds, the response may be 

 regarded as negative, and when it reacts to an odor within 60 

 seconds, the response may be called positive. As a control, an 

 empty and odorless vial was now and then placed under the 

 insects in the same manner. If by chance a beetle moved while 

 the control test was being made, its behavior was different from 

 that observed when odors were used. Only the first responses 

 have been recorded and in all cases where there was the least 



