The Structure and Special Physiology of Insects 27 



come into actual contact with the special taste nerves, it is obvious 

 that insects, to taste solid foods, have first to dissolve particles of these 

 foods in the mouth-fluids, and that the taste-organs have to be situated 

 in the mouth or so that they can be brought into it to explore the food, as 

 are the movable, feeler-like palpi. What experimentation on the sense of 

 taste in insects has been carried on shows that certain insects certainly taste 

 food substances, and indicates that the sense is a common attribute of all 

 insects. Lubbock's many experiments with ants, bees, and wasps present 

 convincing proof of the exercise of the taste sense by these insects. Forel 

 mixed morphine and strychnine with honey, which ants, attracted by the 

 honey smell, tasted and refused. Will's experiments show that wasps 

 recognize alum and quinine by taste. He found bees and wasps to have 

 a more delicate gustatory sense than flies. 



Smell is probably the dominant special sense among insects. It exists 

 at least in a degree of refinement among certain forms that is hardly 

 equalled elsewhere in the animal kingdom. The smelling organs are micro- 

 scopic pits and minute papillae seated usually and especially abundantly 

 on the antennae, but probably also occurring to 

 some extent on certain of the mouth-parts. The 

 fact that the antennae are the principal, and in 

 many insects the exclusive, seat of the olfactory 

 organs has been proved by many experiments in 

 removing the antennae or coating them with par- 

 affine. Insects thus treated do not find food or 

 each other. As substances to be smelled must 

 actually come into contact, in finely divided con- 

 dition, with the olfactory nerve-element, these 

 pits and papillae are arranged so as to expose 

 the nerve-end and yet protect it from the 

 ruder contact with obstacles against which the 

 antenna; may strike. It is certain that most 

 insects find their food by the sense of smell, and 

 the antenna of a carrion-beetle (Fig. 54) shows 

 plainly the special adaptation to make this sense 

 highly effective. On the "leaves" of each antenna 

 of June-beetles nearly 40,000 olfactory pits occur. 

 Some of the results of experimentation on smell 

 indicate a delicacy and specialization of this sense 

 hardly conceivable. A few examples will illustrate 

 this. It is believed that ants find their way back 

 to their nests by the sense of smell, and that 

 they can recognize by scent among hundreds of individuals taken from 



FIG. 54. Antenna of a 

 carrion-beetle with- the 

 terminal three segments 

 enlarged and flattened, 

 and bearing many smell - 

 ing-pits. (Photomicro- 

 graph by George O. Mit- 

 chell; much enlarged.) 



