22 The Naturalist in Nicaragua 
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 those ants which hunt singly, and which 
have the eyes greatly developed. The imperfection of eye- 
sight in the Ecitons is an advantage to the community, and 
to their particular 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 dis- 
cover at a distance. The Ecitons and most other ants 
follow each other by scent, and, I believe, they can com- 
municate the presence of danger, of booty, or other intelli- 
gence, to a distance by the different intensity or qualities of 
the odours given off. I one day saw a column of Eciton 
hamaia running along the foot of a nearly perpendicular 
tramway cutting, the side of which was about six feet high. 
At one point I noticed a sort of assembly of about a dozen 
individuals that appeared in consultation. Suddenly one 
ant left the conclave, and ran with great speed up the per- 
pendicular face of the cutting without stopping. It was 
followed by others, which, however, did not keep straight on 
like the first, but ran a short way, then returned, then again 
followed a little further than the first time. They were 
evidently scenting the trail of the pioneer, and making it 
permanently recognisable. These ants followed the exact 
line taken by the first one, although it was far out of sight. 
Wherever it had made a slight detour they did so likewise. 
I scraped with my knife a small portion of the clay on the 
trail, and the ants were completely at fault for a time which 
way to go. Those ascending and those descending stopped 
at the scraped portion, and made short circuits until they 
hit the scented trail again, when all their hesitation vanished, 
and they ran up and down it with the greatest confidence. 
On gaining the top of the cutting, the ants entered some 
brushwood suitable for hunting. In a very short space of 
