25° THE NATURE-STUDY REVIEW [i, 6, nov. 1905 



In four nests, I kept brown ants that were all of one colony, 

 and sequestered at their hatching. One of these groups had been 

 segregated three years, one group had been segregated two years, 

 one group had been segregated one year, and one group consisted 

 of newly hatched ants, when I introduced marked members of 

 each group, one ant at a time, into each of the other three nests. 

 In every case the older ants remembered the odor of the younger 

 ants, and received them amicably, while the younger ants, never 

 having smelled the odor borne by the older ants, fought the visi- 

 tors with plain intent to kill. This experiment showed that the 

 brown ants had a power of memory extending to three vears. 

 It is probable that ants recognize at any time during their lifetime 

 an odor with which they have once become familiar. 



These experiments also indicate that the ants do not recognize 

 one another by the contour, for their form had not changed dur- 

 ing the period of separation. Had they means of conversation 

 relating to the past, we must suppose that they would at their 

 second meeting, have talked of old times instead of tearing each 

 other. The only probable explanation of their behavior is that 

 they were repelled by an unknown odor in some of these cases, 

 and were pleased by a recognized odor in other cases. 



Workers of one of the species employed in my experiments 

 are but an eighth of an inch in length, while the head is but a 

 quarter of the total length, and the brain within the head is so 

 small as to be invisible except with the aid of a lens. If a brain 

 so small can record an impression of an odor and act on that 

 impression years afterward, this fact indicates to us that but few 

 particles of matter are required as a seat for the mental powers. 



We do not know whether the ants exercise reason and imagi- 

 nation ; but they certainly have power of memory which is a 

 foundation for all the higher psychic activities. 



Under the dominance of the sense of smell and the power of 

 memory, every ant acts upon individual experience. But there 

 are differences in the character of ants of the same variety and 

 of the same external structure. Some have stronger local attach- 

 ments than have others, and adhere more closely to an old home. 

 Some are more assiduous in their care of the developing young. 

 Some are distinguished by exceeding truculence, while others are 

 surpassingly amiable. Some are sluggards, while others are 

 markedly enterprising. 



