Sensory Discrimination : the Chemical Sense 87 



where preference did not. Another criticism urged against 

 Graber's experiments is that the odors used were too strong 

 and irritating. The insects displayed choice between odors 

 even when their antennae were removed ; but there is much 

 evidence to show that the antennae 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 stimu- 

 lation, fail to do so when deprived of antennae (130). Inter- 

 esting "compensatory movements" have been seen in silk- 

 worm moths with one antenna removed ; they turned, that is, 

 in the direction of the remaining antenna (219). We shall 

 note movements of this class later in insects with one eye 

 blackened, and in fish with one auditory nerve cut. The 

 exploring movements of the antennae which certain insects 

 make in seeking a proper place to lay their eggs in have been 

 taken as evidence of the smell function of these organs (324). 

 It may be, then, that the reactions of insects without antennae 

 observed by Graber were due rather to the irritating than 

 to the properly olfactory character of the stimuli. 



The function of the chemical sense in the mating processes 

 of insects is one of the most remarkable phenomena connected 

 with the sensory reactions of animals. Forel says he had a 

 female Saturnia moth shut up in his city room, and that 

 within a short time a number of males came and beat against 

 the window (130). Riley hatched in Chicago some moths 

 from the Ailanthus silkworm, which were carefully confined. 

 No other specimens were known to exist within hundreds of 

 miles. A virgin female was put in a wicker cage on an ailan- 

 thus tree, and a male, with a silk thread tied around the abdo- 

 men for identification, was liberated a mile and a half away. 

 The next morning the two were together (363). 



