4o6 'Journal of Coniparntivc Neurology and Psychology. 



Explanation of Table VIII. 



Column I. The number of vibrations per second. 



Column 2. A colony of Formica fusca var. subsericea Say, containing three fertile females and 

 about two hundred neuters. 



Column 3. A colony of Formica fusca var. subsericea Say, containing about two hundred neuters 

 and no fertile females. 



Column 4. A mixed colony of Formica sanguinea Latrl. and Formica fusca. This colony contained 

 about two hundred neuters, over two-thirds of which were fuscas. No females were present. 



Column 5. A few workers of Formica fusca var. subsericea Say, the antennae of which had been 

 removed two days before. 



Some may think the response of these ants was the result of 

 tactile stimuli caused by shaking of the nest by the sound wave. 

 To me it does not seem possible for the nests to have vibrated in 

 response to each of so wide a range of pitches. However, to 

 meet that objection, the following experiment was devised. I 

 obtained some felt cloth two mm. thick and placed two layers of 

 it in the bottom of each of the living chambers of a Janet nest. 

 This nest rested on cotton placed on the table the legs of which 

 rested on wads of cotton. After the ants had become accustomed 

 to their carpeted floor, various sounds were made. This experi- 

 ment was tried upon both Formica fusca var. subsericea Say 

 and Formica sanguinea Latr. It is important to note that even 

 with the false felt bottom to stand on, the ants could not reach 

 the top of the nest with their antenna?. In each case the ants 

 responded to the sound in the same manner as has been described 

 above. Since the felt would prevent nest tremors reaching the 

 ants, the response, it seems to me, must have been to air vibrations 

 which the human ear would sense as sounds. 



At present I have housed in a Janet nest a small colony of 

 Camptonus herculeano-ligniperdus. This colony consists of eight 

 winged females and about twice as many neuters. Usually one 

 of the neuters mounts guard in the outer doorway. Whenever 

 sounds similar to those mentioned above are made, this guard 

 shows marked evidence of being disturbed. Under such condi- 

 tions it makes agitated movements with its antennae and often 

 snaps with its jaws right and left. If the noise is continued, the 

 guard is apt to rush back into the nest. 



Undoubtedly, artificial colonies of each of these species of ants 

 respond in a pronounced manner to atmospheric vibrations which 

 to the human ear would be sounds. 



When, however, I tested ants that w^ere moving about outside 

 the nest, I obtained no such marked reactions. Often I could 



