178 ESSAYS OF A BIOLOGIST 



nals, when ants were simple unsophisticated folk, 

 barely emerged from entomological barbarism. 

 Some stayed at home to look after the young brood 

 and tend the houses, others went afield to forage. It 

 was not long before they discovered that the days 

 differed in length. At one season of the year they 

 found the days insufferably long; they must rest 

 five or six times if they were, by continuing work 

 while light lasted, to satisfy their fabulous instinct 

 for toil. At the opposite season, they needed no rest 

 at all, for they only carried through a fifth of the 

 work. This irregularity vexed them: and what is 

 more, time varied from day to day, and this hindered 

 them in the accurate execution of any plans. 



But as the foragers talked with the household serv- 

 ants, and with those of their own number who 

 through illness or accident were forced to stay in- 

 doors, they discovered that the home-stayers noticed 

 a much slighter difference in time between the sea- 

 sons. 



It is easy for us to see this as due to the simple 

 fact that the temperature of the nest varies less, 

 summer and winter, than does that of the outer air: 

 but it was a hard nut for them, and there was much 

 head-scratching. It was of course made extremely 

 difficult by the fact that they were not sensitive to 

 gradual changes in temperature as such, the change 

 being as it were taken up in the altered rate of liv- 

 ing. But as their processes of thought kept pace in 



