Four heads of birds: a swan, a polyphemus, a wild duck and a pelican. Drawing, c. 1789.

In applying the study of physiognomy to the animal world, Lavater asserts a "proportional difference of force and form. ... From the insect invisible to the naked eye, up to the elephant, is not the gradation of internal and external character perpetually in exact relation?" (vol. II.i. p. 99)