Haeckel's Evolution of Man. This plate shows the embryos of four mammals in the three corresponding stages: of a Hog (H), Calf (C), Rabbit (R), and a Man (M). The conditions of the three different stages of development, which the three crossroads (I,II,III) represent, are selected to correspond as exactly as possible.

Licence: Public Domain Mark

Credit: Haeckel's Evolution of Man. This plate shows the embryos of four mammals in the three corresponding stages: of a Hog (H), Calf (C), Rabbit (R), and a Man (M). The conditions of the three different stages of development, which the three crossroads (I,II,III) represent, are selected to correspond as exactly as possible. Wellcome Collection. Source: Wellcome Collection.