740 



Bulletin American Museum of Natural History. [Vol. XXIII, 



Some well-developed means of intercommunication would seem to be 

 necessary for ants like Atta texana which live in great colonies and cooperate 

 so intimately both on their foraging expeditions and in the cultivation of 

 their delicate food plant. I am convinced that this means is supplied by the 

 stridulatory organs which are highly developed in all the castes of the species. 

 As I have shown in a former paper/ the stridulation of the huge females of 

 Atta texana is audible when the insect is held a foot or more from the ear. 

 The male and soldier to be audible must be held somewhat closer, the largest 

 workers still closer, whereas the smaller workers and mimins, though stridu- 

 lating, as may be seen by the rapid movements of the gaster on the post- 

 petiole, are quite inaudible to the human ear. It is probable that all these 



Fig. 15. Portion of fungus garden of Atta tc.rana built up by ants in confinement. (Photo- 

 graph by Messrs. Brues and Melander.) 



differences in the rate of vibrations, or humanly speaking, of pitch, corre- 

 lated as it is with a differentiation in the size and functions of the various 

 castes, is a very important factor in the cooperation of these insects, espe- 

 cially in the often widely separated subterranean cavities in which they 

 spend so much of their lives. Miss Fielde and Prof. Parker ^ have recently 

 given good reasons for concluding that these vibrations are transmitted 

 through the soil or other solids and not through the air, and that they are 

 therefore perceived by the ants through their legs as tactile rather than as 



1 Ethological Observations on an American Ant (Leptothorax Emersoni Wheeler).. Arch, 

 f. Psychol, u. Neurol., II, 1903, p. 19, foot-note. 



2 Tlie Reactions of Ants to Material Vibrations. Proc. Acad. Nat. Sci. Pliila., Sept. 1904, 

 pp. 642-650. 



