Ch. II.] EYES OF THE ECITOXS. 23 



many other birds build in holes of trees or in the 

 ground, and these, with their heads ever turned to the 

 only entrance, are in the best possible position to pick 

 off the solitary parties when they first approach, and 

 thus prevent them from carrying to the main army 

 intelligence about the nest. Some of these birds, and 

 especially the toucans, have bills beautifully adapted for 

 picking up the ants before they reach the nest. Many 

 of the smaller birds build on the branches of the bulPs- 

 horn thorn, which is always thickly covered with small 

 stinging honey-eating ants, that would not allow the 

 Ecitons to ascend these trees. 



Amongst the mammalia the opossums can convey 

 their young out of danger in their pouches, and the 

 females of many of the tree-rats and mice have a hard 

 callosity near the teats, to which the young cling with 

 their milk teeth, and can be dragged away by the 

 mother to a place of safety. 



The eyes in the Ecitons are very small, in some of 

 the species imperfect, and in others entirely absent; 

 in this they differ greatly from the Psciidomyrma ants, 

 which hunt singly and which have the eyes greatly 

 developed. The imperfection of eyesight in the Ecitons 

 is an advantage to the community, and to their par- 

 ticular mode of hunting. It keeps them together, and 

 prevents individual ants from starting off alone after 

 objects that, if their eyesight were better, they might 

 discover at a distance ; the Ecitons and most other ants 

 follow each other by scent, and, I believe, they can 

 communicate the presence of danger, of booty, or other 

 intelligence, to a distance by the different intensity or 

 qualities of the odours given off. I one clay saw a column 



