Architecture in the Animal Kingdom. 113 



them to withdraw from these repeated disturbances by 

 closing up and concealing their nest. 



Professor Aug. Forel 1 relates that he had brought 

 home from Algeria a colony of Myrmecocystus altis- 

 quamis and placed it in his garden at Zuerich; but 

 owing to the trouble caused them by the small ants 

 Lasius niger and Tetramorium caespitum they grad- 

 ually modified their usual manner of nest construction. 

 Under normal circumstances this Myrmecocystus 

 species has wide open nest entrances; in this case, 

 however, they were contracted to afford greater pro- 

 tection against the thievish visitors, and finally they 

 were almost entirely closed up. This instance is sim- 

 ilar to the one recorded above of colony 36 of F. 

 sanguined, and is psychologically to be explained in 

 the same way. The repeated disagreeable experiences 

 caused to the ants by the troublesome strangers 

 induced the Myrmecocysti, contrary to their former 

 habits, to close up and to conceal their nest. As 

 Forel points out, these facts afford irrefutable evidence 

 of the great plasticity of ant instinct. For, this 

 instinct is not merely a nervous mechanism' forced to 

 operate along uniform lines ; it includes sensitive cog- 

 nition and appetite, which are not only of an organic 

 but also of a psychic nature. Thus animals are 

 enabled, by new sense perceptions and experiences, 

 to adapt their wonted mode of action to the require- 

 ments of circumstances. This does not, however, 

 compel us in the least to attribute to animals a power 

 of cognition essentially the same as human intelligence ; 



1 ) "Les Formicides de la Province d'Oran" (Lausanne, 1894), p. 

 8; see also "Aperc.u de Psychologic comparee," p. 24, by the same 

 author. 



