THE PLASTIC BEILll'IOR OF ANTS. 533 



fully confirmed by Wasmann. Lubbock, Viehmeyer and, more recently, 

 Turner, have found some evidence that ants may also be guided by the 

 direction of the light rays. Turner, especially, has emphasized this 

 point, but he seems to overlook the fact that it can have only subordi- 

 nate significance, as many of our ants forage as readily at night or 

 in the dark store-rooms of "houses, the holds of ships, etc., as they do 

 in the daylight, that many tropical and desert species are nocturnal at 

 certain seasons, and that others are permanently nocturnal or hypogaeic. 

 We are compelled, therefore, to regard the topochemical, or contact- 

 odor sense as all important in the foraging and homing behavior of 

 ants, although it must be admitted that other senses may be relied upon 

 to some extent. Bethe (1898), with a rather superficial knowledge of 

 the habits of ants and of the literature pertaining to them, has endeav- 

 ored to show that these insects follow the odor trail from and to the 

 nest in a purely reflex manner and therefore neither exhibit nor require 

 even a rudiment of memory. Like a true physiologist, he selected for 

 his studies the first ants that came to hand Lasius nlger, L. cniarginatus 

 and Myrmica scabrinodis all species which adhere closely to their 

 trails and, overlooking Forel's important studies, postulated a " polari- 

 zation " of the paths as more acceptable to the scientific mind than any 

 explanation involving a psychical factor. Wasmann, in a comprehen- 

 sive work on the mental endowment of ants (18990), has adequately 

 demonstrated the falsity of Bethe's position. To this work and to 

 Forel's controversial articles (IQOO-'OI, 1903^ etc.) the reader is 

 referred for the further arguments on the subject. Here it will suffice 

 to quote a passage in which Forel gives some of his reasons for assum- 

 ing the existence of memory in the insects under discussion : " 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 herself about her abductrix, and carry her to the newly 

 selected spot. The latter then also finds her way to the original 

 nest, and each carry back another companion, etc. The memory 

 of the suitable 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 companion, to .this very spot. The slave-making ants 

 (Polyergus ) undertake predatory expeditions, led by a few workers, 

 who for days and weeks previously have been searching the neigh- 

 borhood 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 

 proper direction by rapidly pushing ahead. Then the pupae of the 



