Such a teleology is, it is obvious, indistinguishable in principle from the position in which Kant leaves us. It is the position adopted by Driesch himself in his earlier _Analytische Theorie_, but abandoned in the _Vitalismus_ in favour of a theory of ‘psychoids’. Now quite apart from the meaning which Aristotle may or may not have intended to convey, there are grave objections to this belief. This ‘psychoid’, to which the name ‘entelechy’ is surely misapplied, this rudimentary feeling and willing, which is aware of the form it desires to produce, must be psychically at least as complex as the phenomena it is designed to account for, and stands, therefore, as much in need of explanation as they; as Kant has observed, this will involve us at once in an infinite series of such entities. In fact it is only a photograph of the problem, and not a solution at all. Again, when we ask what the _modus operandi_ of this cause is, we get no reply either from Driesch or from any other neovitalist. The objection that the intervention of a psychical cause in a physical process is unintelligible, an objection which would probably appeal to many, may be waived, for in the last resort the connexion between any--even simple mechanical--causes and effects is equally hard to understand. It may, however, be doubted whether these entities are not being multiplied beyond necessity, and whether the progress of science would not be better served by an adherence to a simpler philosophy. But even when it has discarded the psychoid we find vitalism still denying the possibility of mechanical explanation, still preaching the autonomy of the organism. The ‘dynamic’ teleology of Driesch has only disappeared to be replaced by the metaphysical doctrine of the final cause. We may point out, perhaps, in passing, that the organism is by no means as autonomous as might be desired. The end towards which the creature strives, the maintenance and reproduction of its own specific form, is not a constant _terminus ad quem_, for species are as mortal as individuals: nor is it always achieved; the autonomy of a worm, which, bisected in a certain way, regenerates a tail instead of a head, or of a frog, which, after a particular injury, develops six legs instead of two, has surely renounced its rights. But, setting this aside, it must be seriously questioned whether any good purpose is served in biological discussion by decrying the value of mechanical conceptions or by confounding two distinct orders of thought. The questions are grave ones: for the issue at stake is no less than the existence of physiology as the science of the causes of living activities.