476 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



mentary canal certainly can not serve such a function except when 

 corrosive or caustic substances are eaten. 



After once refusing foods which contain undesirable substances 

 emitting weak odors bees seem to know these foods and seldom eat 

 any more of them unless forced to partake of them by the removal of 

 the foods they like better. 



In conclusion, it may be said that the olfactory sense in the honey- 

 bee is highly developed and that it serves as an olfactory and gusta- 

 tory perception combined. 



THE SENSE OF TOUCH. 



Excluding spiders, perhaps no other class of animals (including 

 man) has the sense of touch so highly developed; this is particularly 

 true with those insects — as, for example, ants and bees — that carry 

 their eggs in their mandibles or jaws from place to place. The 

 eggs are almost miscroscopic, and so extremely delicate that the least 

 rough handling of them prevents them from hatching, but the com- 

 paratively large and hard jaws of ants and bees are so wonderfully 

 controlled by the sense of touch that the eggs are handled without the 

 least injury. 



Relative to spiders, their sense of touch seems to be of a different 

 nature, and in this particular line of evolution there is no comparison. 

 A female orb-weaver at the center of her web can tell friend from 

 foe, male from female of her species, an insect suitable for food from 

 one not suitable, an insect of a certain size from an inanimate object 

 of the same size, and she can also distinguish between sizes of any 

 two objects which happen to fly or to be thrown into her web. This is 

 all accomplished by touch vibrations passing along the radii of the 

 orb on which the legs of the female spicier rest. Moreover, during 

 courtship of spiders this system of touch vibrations is utilized as a 

 means of signals to inform the male concerning the proper mood of 

 the female for mating — but pity the dwarfed male should he mis- 

 interpret her signals, for instantly she pounces upon him and devours 

 him without showing the least mercy. 



In man the sense of touch is accomplished by touch corpuscles 

 lying in the skin, but since insects have an exo-skeleton, a different 

 system has been evolved. In them touch or tactile hairs, connected 

 with nerves, take the place of touch corpuscles in us. Thus, when the 

 air blows against these hairs or an object touches them the stimuli 

 are transmitted through the hairs and their nervous connections to the 

 brain, where the impulses are interpreted as touch. 



In insects, as in man, all parts of the external anatomy are not 

 equally sensitive to touch stimuli. In man the tips of the tongue 

 and fingers are the most sensitive, while in the honeybee the tips of 



