5 10 .I\TS. 



In idy. It is probable, however, that the odor stimulates the delicate 

 end organs onlv when it is dissolved in the thin film of glandular secre- 

 tion covering the antennal club. When the antennae actually touch the 

 surface of a bod}-, however, the ant, in all probability, receives both 

 tactile and olfactory stimuli, and these probably fuse to produce a 

 single sensation, which Forel calls the topo-chemical, or contact-odor 

 sensation. He believes, therefore, that the ant has a sense of odor- 

 shape. To make this clear he suggests that we fancy ourselves to be 

 blind or in total darkness and in possession of delicate olfactory organs 

 in our finger-tips. Then, if we moved about, touching objects to the 

 right and left along our path, our environment would appear to us to 

 be made up of shaped odors, and we should speak of smells that are 

 spherical, triangular, pointed, etc. Our mental processes would be 

 largely determined by a world of chemical configurations, as they are 

 now by a world of visual (/. c., color) shapes. Blind ants are, of 

 course, permanently in the condition here described, and as all other 

 ants spend most of their time in the dark recesses of the nest, and. with 

 the exception of very few species, rely but little on their eyesight, we 

 can see how different must be our own mental processes from those of 

 these insects. 



In order to understand many of the commonest reactions of ants, 

 such as the recognition of friends and foes, the homing instincts of the 

 worker and the development of certain peculiarities of myrmecophiles, 

 we must suppose that ants have not only extremely acute powers of 

 odor-discrimination, but no less extraordinary powers of odor-associa- 

 tion. Even the degenerate human olfactories can detect the different 

 species and in some cases even the different castes of ants (Ecitoii ) by 

 their odors, but these insects carry the discrimination much further. They 

 not only differentiate the innate odors peculiar to the species, sex. caste 

 and individual and the adventitious or " incurred " odors of the nest and 

 environment, but, according to Miss Fielde, they can detect " progres- 

 sive odors," due to change of physiological condition with the age of 

 the individual. She believes that " as worker ants advance in age their 

 progressive odor intensifies or changes to such a degree that they may 

 be said to attain a new odor every two or three months." Miss Fielde 

 is also convinced that different antennal joints are specialized for the 

 perception of different odors. This conclusion was reached by cutting 

 off the joints one at a time and studying the subsequent behavior of the 

 ant. She says: "The organ discerning the nest-aura, and probably 

 other local odors, lies in the final joint of the antenna, and such odors 

 are discerned through the air; the progressive odor or the incurred 

 odor is discerned by contact, through the penultimate joint ; the scent 



