ANTS AND SOME OTHER INSECTS. ig 



of a new flight of orientation. An animal, however, certainly can- 

 not forget without having remembered. 



The topochemical antennal sense also furnishes splendid proofs 

 of memory in ants, bees, etc. An ant may perform an arduous 

 journey of thirty meters from her ruined nest, there find a place 

 suitable for building another nest, return, orienting herself by 

 means of her antennae, seize a companion who forthwith rolls her- 

 self about her abductrix, and is carried to the newly selected spot. 

 The latter then also finds her way to the original nest, and both 

 each carry back another companion, etc. The memory of the suit- 

 able nature of the locality for establishing a new nest must exist in 

 the brain of the first ant or she would not return, laden with a com- 

 panion, to this very spot. The slave-making ants (Polyergus} un- 

 dertake predatory expeditions, led by a few workers, who for days 

 and weeks previously have been searching the neighborhood for 

 nests of Formica fusca. The ants often lose their way, remain 

 standing and hunt about for a long time till one or the other finds 

 the topochemical trail and indicates to the others the direction to 

 be followed by rapidly pushing ahead. Then the pupae of the For- 

 mica fusca nest, which they have found, are brought up from the 

 depths of the galleries, appropriated and dragged home, often a 

 distance of forty meters or more. If the plundered nest still con- 

 tains pupae, the robbers return on the same or following days and 

 carry off the remainder, but if there are no pupae left they do not 

 return. How do the Polyergus know whether there are pupae re- 

 maining? It can be demonstrated that smell could not attract them 

 from such a distance, and this is even less possible for sight or any 

 other sense. Memory alone, i. e., the recollection that many pupae 

 still remain behind in the plundered nest can induce them to re- 

 turn. I have carefully followed a great number of these predatory 

 expeditions. 



While Formica species follow their topochemical trail with 

 great difficulty over new roads, they nevertheless know the imme- 

 diate surroundings of their nest so well that even shovelling away 

 the earth can scarcely disconcert them, and they find their way at 

 once, as Wasmann emphatically states and as I myself have often 



