SOURCE: "Ernst Heinrich Haeckel," in Living Biographies of Great Scientists, Nelson Doubleday, Inc., 1941, pp. 233-44.

In the following excerpt, Thomas and Thomas offer an account of Haeckel's professional and personal life .

"In a recent microscopical lecture," wrote Haeckel to his parents during his college days at Würzburg, "Professor Leydig suddenly stopped and pointed to me with the greatest astonishment. 'I've never seen the like of it in my life!' he cried. This young man can look through the microscope with the left eye while with the right eye he can draw what he sees . . .' This curiosity in my physical make-up," continued Haeckel, "is of the utmost importance in the study of natural history."

Together with his double physical vision Haeckel was blessed with a double mental vision. One half of him was an observant scientist; the other half, an imaginative artist. He was equally adept...