Lorenz split a  large clutch of greylag goose eggsinto two  groups.

One was allowed to hatch normally and the goslings followed their mother around.

Lorenz had the second group of eggs incubated and then arranged it so that he  was the first thingthe goslings saw  when  they hatched. From then on they followed  him everywhere.

The goslings had formed a picture (imprint) of  the object they were to follow.

When he marked the goslings as to which group of eggs they had hatched from and  then let them outtogether from an upturned  box, each gosling went straight toits  'mother figure'. Lorenz' goslings showed no recognition of  their real mother.