Page:Mind (Old Series) Volume 9.djvu/42

 30 J. S. HALDANE. that the result is determined by, or is the effect of, the process, for it appears to be just as true that the process is determined by the result. Now this being so, it appears to me that the analogy between the nervous system and a machine can 110 longer by any possibility be held to. The action of a machine is determined from behind. That is to say, every one of its movements can be traced back to a cause antecedent in time, and in this way explained. But this is not true of the movements which we have been considering in the case of the earthworm ; for the apparent cause appears to be as much effect as cause of the apparent effect. I shall, however, return to this matter presently. Such behaviour as that of the earthworm in these experi- ments is only one example of a kind of behaviour which may be observed in the case of other organisms. Since the word ' intelligent ' carries with it a reference to consciousness, I shall call this kind of behaviour ' purposive ' rather than ' intelligent '. But it is not only where the nervous system is concerned that purposive behaviour may be observed ; for such be- haviour is evident enough in the case of other tissues. Attention has been drawn elsewhere l to the significance of what occurs in the healing of wounds, especially among the lower animals. And it was pointed out that in the case of, say, the reproduction, after -amputation, of the limb of a newt, it is not possible to explain on mechanical principles the behaviour of the cells which are concerned in the process. As the phenomena referred to may be passed over without their significance being realised, it may be well to indicate more particularly in what respects they are significant. Let us suppose that the limb is amputated half way up the thigh : the cells near the surface of the stump work together by dividing and developing in various ways, so as to reproduce the limb. Supposing now that the line of amputation is oblique or irregular, this does not affect the result. The cells concerned in the process allow for the irregularity. If, for instance, two-thirds of the extensors of the knee, half of the thigh bone, and a third of the ham- string muscles, are amputated, the missing part of each of these structures is nevertheless reproduced in its proper proportion. Now were the behaviour of the cells determined by anything of the nature of mechanisms within them, we should find that they did their work in the same way as machines do their work that is to say, blindly. We should, 1 Essays in Philosophical Criticism, p. 54.