Sensory Discrimination: The Chemical Sense 91 



a food sense. There has been but little evidence of the 

 development of qualitative discrimmation within the sense 

 itseK. That is, while in many cases an animal can appar- 

 ently distinguish the edible from the inedible, and gives 

 negative reactions to irritating chemicals, one would hardly 

 be justified in saying that it possesses more than one food-^ 

 sensation quaKty ; while in our own case, of course, though 

 we make comparatively little use of the sense of smell, the 

 qualitative discriminations possible by its means are 

 many. But we come now to a group of animals where 

 there appears a remarkable development of qualitative 

 variety in the sensations resulting from chemical stimula- 

 tion; namely, the Insecta. As the reactions of animals 

 to mechanical stimulation, on the other hand, offer evi- 

 dence of little qualitative difference in the accompanying 

 sensations, we shall give but slight attention to them in 

 what follows. 



To begin with, there is evidence that taste and smell are 

 distinct in many insects. The water beetle Dytiscus mar- 

 ginalis, found apparently unresponsive to food at a dis- 

 tance, will bite with especial eagerness at filter paper soaked 

 in what Nagel calls "a pleasant solution" (522). Ants 

 fed honey mixed with strychnin will taste it and then 

 stop, and will do this even when the antennae and mouth 

 palpi are removed, indicating that the taste organs are 

 in the mouth itself (231). Similar results have been ob- 

 tained from similar tests on wasps, and it has been observed 

 that wasps so treated will hesitate when offered pure honey 

 afterward (786). 



Essenberg (208) found that the water strider, when 

 offered flies which had been soaked, some in quinin and 

 alcohol, some in coal oil, some in ammonia, approached 

 them " carefully," left them, and then returned and devoured 



