Abstract
The purpose of this paper is to draw attention to a similarity between an ancient and a modern theory of living nature. There is no need to present the Aristotelian doctrine in full detail. I must rather apologize for repeating much that is well known. My endeavour is to offer it for comparison, and, incidentally, to clear it from misrepresentation. Uexküll's theory, on the other hand, is little known, and what is given here is an insufficient outline of it. I do not maintain that either doctrine is right. I am fully aware that the problem of the essence of living nature by no means admits of an éasy solution. In offering for consideration the comparison contained in this paper I would go no farther than owning my belief that the two authors here discussed, both thinkers who combine an intensely philosophical outlook with a wide biological experience, are worth the attention not only of the historian of science and philosophy, but also of the student of philosophical biology