92 The Animal Mind 



them, a proceeding which proved fatal in certain instances. 

 The insects would stop and retreat just before reaching a 

 drop of coal oil. 



Vitus Graber tested the reactions of various insects to 

 odors by the method which we called on page 55 the 

 Method of Preference. This was Graber's favorite mode 

 of studying the effect of stimuli upon animals. Applied 

 to olfactory stimuli it consisted in offering a choice between 

 different compartments, containing each a different odor. 

 The animal's power of discrimination was argued from the 

 tendency to choose certain odors rather than others. 

 Such preferences were shown by the insects (268). The 

 method, however, as was noted above, is unsatisfactory, 

 because discrimination might exist where preference did 

 not. Another criticism urged against Graber's experi- 

 ments is that the odors used were too strong and irritating. 

 There is always the possibility that such substances affect 

 other nerves than those of smell. The insects observed by 

 Graber displayed choice between odors even when their 

 antennae were removed. There is much evidence to show 

 that the antennse are the true organs of smell in insects. 

 Various flies and beetles which are in the habit of laying 

 their eggs in putrefying flesh will not react to it when their 

 antennae are removed, and it has been shown that insects 

 which seem to find their mates by response to olfactory 

 stimulation fail to do so when deprived of antennae (231). 

 Interesting "compensatory movements" have been seen 

 in silkworm moths with one antenna removed; they 

 turned, that is, in the direction of the remaining antenna 

 (397). We shall note movements of this class later in 

 insects with one eye blackened, and in fish with one audi- 

 tory nerve cut. The exploring movements of the antennae 

 which certain insects make in seeking a proper place to 



