Architecture in the Animal Kingdom. 137 



between the top-end of the bridge and the cork of the 

 glass was about 2 cm. When exposed to the sun the inside 

 of the glass was generally covered with moisture, and 

 the ants found great difficulty in passing the intermedi- 

 ate space and in getting into the top-nest. Although 

 this state of affairs lasted for weeks, and the ants con- 

 tinued to encounter the same difficulties, it never 

 occurred to them to connect the broad, upper end of 

 the stick with the roof of the front-nest by a bridge 

 of earth. They connected the sides of the stick with the 

 glass by a wall of earth ; gradually they also covered 

 the whole glass-wall with pellets of earth to protect 

 themselves against the rays of the light ; but they 

 never built a bridge at the critical spot, where one was 

 evidently needed and of the greatest importance. The 

 pellets of earth accidentally fastened there were, on 

 the contrary, continually thrown down by the ants 

 that crawled up the road. Thus exactly that spot 

 over which the ants, if they were endowed with any 

 power of thought and reflection, would be expected to 

 build a bridge, was left slippery and smooth, and was 

 still the same after half a year. 



In 1884 I repeatedly made the following experi- 

 ment: In a tiny vessel I suspended some honey or 

 ant-larvae over a nest of F. sanguinea, contained in a 

 large "crystallisator", 1 so that the ants could touch the 

 vessel with their antennae only, but could not reach 

 it except by a very circuitous route. It should have 

 occurred to them to heap up a little earth or some 

 pieces of wood underneath the vessel, in order to form 

 a "bridge" leading directly to the wished for goal. 



>) A low, round glass bowl, covered by a glass plate. 



