Instinctive Behaviour of Ants 91 



the whole army separate in search of nests of 

 black ants. At last a nest of these latter species 

 having been found, a signal is given by striking 

 the forehead of a neighbour; this signal is 

 passed from one red ant to the other, and the 

 army re-forms. On arriving at the black ants' 

 nest a desperate conflict ensues, which ends in 

 the defeat of the negroes; and the red ants 

 then enter the nest and leave it almost in- 

 stantly, each insect holding a larva or pupa in 

 its mandibles, which it carries home with all 

 speed. In the return of the army there is never 

 any hesitation ; the olfactory and visual memory 

 of the outward journey is sufficient to make 

 known to each ant the exact road. Having 

 reached home the red ant hands over the stolen 

 larva to a slave, and as a rule sets off imme- 

 diately to the pillaged nest if it still contains 

 more larvae, or they may put off the return 

 journey until the following day. Forel states 

 this return journey is never made if the pillaged 

 nest has had the whole of the larvae removed; 

 he remarks : ' The fact appears to me to fur- 

 nish irrefutable proof of their memory. They 

 must remember if the pillaged nest still con- 



