During the early twentieth century, the Swiss Zoologist Adolf Naef (1883–1949) established himself as a leader in German comparative anatomy and higher level systematics. He is generally labeled an ‘idealistic morphologist’, although he himself called his research program ‘systematic morphology’. The idealistic morphology that flourished in German biology during the first half of the twentieth century was a rather heterogeneous movement, within which Adolf Naef worked out a special theoretical system of his own. Following a biographical sketch, we present an (...) English translation of a previously unpublished typescript from Naef’s estate, which Naef intended as the introduction to a textbook on Comparative Anatomy for which he was unable to find a publisher before his sudden death in 1949. The typescript contains Naef’s mature thoughts with unprecedented conciseness, focus, and clarity. The density of Naef’s text warrants a historical and contextual explication of its content. (shrink)