in.] DIVISION OF LABOUR INTELLIGENCE. 79 



share in the defence of the nest or other out-of-door work 

 until they are some days old. This seems natural, be- 

 cause at first their skin is comparatively soft ; and it 

 would clearly be undesirable to undertake rough work, or 

 run into danger, until their armour had had time to 

 harden. There are, however, reasons for thinking that 

 the division of labour is carried still further. I do not 

 allude merely to those cases in which there are com- 

 pletely different kinds of workers, but even to the ordi- 

 nary workers. In L. flavus, for instance, it seems 

 probable that the duties of the small workers are some- 

 what different from those of the large ones, though no 

 such division of labour has yet been detected. 



One of the most interesting problems with reference to 

 ants is, of course, to determine the amount of their intelli- 

 gence. In order to test this, it seemed to me that one 

 way would be to ascertain some object which they would 

 clearly desire, and then to interpose an obstacle which a 

 little ingenuity would enable them to overcome. With 

 this object in view, I placed food in a porcelain cup on 

 a slip of glass surrounded by water, but accessible to the 

 ants by a bridge, consisting of a strip "of paper two-thirds 

 of an inch long and one-third wide. Having then put a 

 F. nigra from one of my nests to this food, she began 

 carrying it off, and by degrees a number of friends came 

 to help her. I then, when about twenty-five ants were 

 so engaged, moved the little paper bridge slightly, so as 

 to leave a chasm just so wide that the ants could not 

 reach across. They came to the edge and tried hard 

 to get over, but it did not occur to them to push the 

 paper bridge, though the distance was only about one- 

 third of an inch, and they might easily have done so. 



