XVI] THE PROBLEM OF ADAPTATION 673 



far above the region of mere hypothesis, for we have to deal with 

 questions of mechanical efficiency where statical and dynamical 

 considerations can be applied and established in detail. The 

 naval architect learns a great part of his lesson from the investi- 

 gation of the stream-lines of a fish ; and the mathematical study 

 of the stream-lines of a bird, and of the principles underlying the 

 areas and curvatures of its wings and tail, has helped to lay the 

 very foundations of the modern science of aeronautics. When, 

 after attempting to comprehend the exquisite adaptation of the 

 swallow or the albatross to the navigation of the air, we try to 

 pass beyond the empirical study and contemplation of such 

 perfection of mechanical fitness, and to ask how such fitness came 

 to be, then indeed we may be excused if we stand wrapt in wonder- 

 ment, and if our minds be occupied and even satisfied with the 

 conception of a final cause. And yet all the while, with no loss 

 of wonderment nor lack of reverence, do we find ourselves con- 

 strained to believe that somehow or other, in dynamical principles 

 and natural law, there lie hidden the steps and stages of physical 

 causation by which the material structure was so shapen to its 

 ends*. 



But the problems associated with these phenomena are 

 difficult at every stage, even long before we approach to the 

 unsolved secrets of causation ; and for my part I readily confess 

 that I lack the requisite knowledge for even an elementary 

 discussion of the form of a fish or of a bird. But in the form of 

 a bone we have a problem of the same kind and order, so far 

 simplified and particularised that we may to some extent deal 

 with it, and may possibly even find, in our partial comprehension 

 of it, a partial clue to the principles of causation underlying this 

 whole class of problems. 



Before Ave speak of the form of a bone, let us say a word about, 

 the mechanical properties of the material of which it is built f, in 



* Cf. Professor Flint, in his Preface to Affleck's translation of Janet's Cau-ies 

 finales: "We are, no doubt, still a long way from a mechanical theory of organic 

 growth, but it may be said to be the quaesitmn of modern science, and no one 

 can say that it is a chimaera." 



t Cf. Sir Donald MacAlister, How a Bone is Built, Emjl. III. Mag. 1884. 



T. G. 43 



