ANTS AND SOME OTHER INSECTS. 37 



in all the other provinces of organic life. Notwithstanding all the 

 differences presented by animal organisms and the conditions of 

 their existence, the psychic functions of the nerve-elements seem 

 nevertheless, everywhere to be in accord with certain fundamental 

 laws, even in the cases where this would be least expected on ac- 

 count of the magnitude of the differences. 



APPENDIX. 

 THE PECULIARITIES OF THE OLFACTORY SENSE IN INSECTS. 



Our sense of smell, like our sense of taste, is a chemical sense. 

 But while the latter reacts only to substances dissolved in liquids 

 and with but few (about five) different principal qualities, the 

 olfactory sense reacts with innumerable qualities to particles of the 

 most diverse substances dissolved in the atmosphere. Kven to our 

 relatively degenerate human olfactories, the number of these odor- 

 qualities seems to be almost infinite. 



In insects that live in the air and on the earth the sense of 

 taste seems to be located, not only like our own, in the mouth- 

 parts, but also to exhibit the same qualities and the corresponding 

 reactions. At any rate it is easy to show that these animals are 

 usually very fond of sweet, and dislike bitter things, and that they 

 perceive these two properties only after having tasted of the re- 

 spective substances. F. Will, in particular, has published good 

 experiments on this subject. 



In aquatic insects the conditions are more complicated. Nagel, 

 who studied them more closely, shows how difficult it is in these 

 cases to distinguish smell from taste, since substances dissolved in 

 water are more or less clearly perceived or discerned from a dis- 

 tance by both senses and sought or avoided in consequence. Nagel, 

 at any rate, succeeded in showing that the palpi, which are of less 

 importance in terrestrial insects, have an important function in 

 aquatic forms. 



In this place we are concerned with an investigation of the 

 sense of smell in terrestrial insects. Its seat has been proved to be 



