Based on Dr Harry Harlow's cruel research on monkeys: the image is meant to depict a reversal in their fortunes. The surrogate mother has been hanged from a tree. The monkeys have been freed from their cage and it is now occupied by Dr Harlow. A large breast has been provided for the big monkey and the smaller ones are waiting for their turn.
Postcards of this image and The Schizoid Traveller are available free of charge to anyone who is interested enough to ask for a few