In this whole question there is danger of extending our own experience as agents in the constructing of products useful to ourselves, to the organic world, in attempting to account for the way in which the useful characters of organisms have arisen. We see a ship being built, and we know that when it is finished it will be useful. We explain its building by its future usefulness,--that is, we explain the process as the result of human teleology. But have we any right to extend this principle to the organic world, and infer that processes are there carried out _because_ they will ultimately be useful to the individual in which they take place? Unconsciously we have shifted our point of view. The ship does not build itself, and the final result of the building is of no use to the ship. On the contrary, the organism does build itself and the result is useful only to itself. Unless we suppose that some external agent acting as we do ourselves directs the formative processes in animals and plants, we are not justified in extending our experience as directive agents to the construction of the organic world; and if we are not justified in drawing such a conclusion, since the organism by no means always responds adaptively, and in many cases very badly and incompletely, then, it seems to me, we must look for another point of view. In connection with his work on the regeneration of the eye of the salamander, Gustav Wolff (’93) has made some sweeping statements in regard to the phenomenon of adaptation. “Purposeful adaptation is that which makes the organism an organism. It is this adaptation that appears to us as the most characteristic property of all living things. We can think of no organism without this characteristic.” In another place he states, “...we recognize that every explanation that presupposes the living being, every post-vital explanation of organic adaptation, presupposes in every case that which it attempts to explain; we recognize that the explanation of adaptation must coincide with the explanation of life itself.” There is, perhaps, some truth in this statement, but, on the other hand, Wolff has, I think, shot somewhat over the mark. As Fischel (1900) has pointed out, the response is sometimes not adaptive, as when two lenses develop in the same eye in the salamander; and, we may add, as when an antenna develops in certain crustacea in place of an eye, or as when a tail develops instead of a head, or a head in place of a tail. In the light of these facts, it is, I think, going too far to assert that the power of living things to respond adaptively to changes in themselves or in their environment is synonymous with life itself. All that we can fairly claim is that in several cases living forms have been shown to be able to _complete themselves_, and this may be _interpreted_ as an adaptive response. It would carry us far beyond the scope of the present volume to discuss the