DOES A HEN KNOW THAT CHICKENS WILL COME OUT OF HER EGGS?
It may possibly be that in some cases an animal of the highest type, such as a dog, may notice, after a number of times, that certain conequences follow upon its instinctive actions. But it is very unlikely that the hen, whether it be the first time or the twentieth time that she sits, has any idea except simply that things like eggs are very good to sit on. This is true, even though she is glad to see chickens when they come.
The Children’s Encyclopedia, Vol. 2, The Education Book Company Limited, London, E.C.4