CHAPTER XVI 



ON FORM AND MECHANICAL EFFICIENCY 



There is a certain large class of morphological problems of which 

 we have not yet spoken, and of which we shall be able to say but 

 Uttle. Nevertheless they are so important, so full of deep theoretical 

 significance, and so bound up with the general question of form 

 and its determination as a result of growth, that an essay on 

 growth and form is bound to take account of them, however im- 

 perfectly and briefly. The phenomena which I have in mind are 

 just those many cases where adaptation in the strictest sense is 

 obviously present, in the clearly demonstrable form of mechanical 

 fitness for the exercise of some particular function or action which 

 has become inseparable from the life and well-being of the organism. 



When we discuss certain so-called "adaptations" to outward 

 circumstance, in the way of form, colour and so forth, we are often 

 apt to use illustrations convincing enough to certain minds but 

 unsatisfying to others — in other words, incapable of demonstration. 

 With regard to coloration, for instance, it is by colours "cryptic," 

 "\Yarning," "signalling," "mimetic," and so on*, that we prosaically 

 expound, and slavishly profess to justify, the vast AristoteUan 

 synthesis that Nature makes all things with a purpose and "does 

 nothing in vain." Only for a moment let us glance at some few 

 instances by which the modern teleologist accounts for this or that 

 manifestation of colour, and is led on and on to beUefs and doctrines 

 to which it becomes more and more difficult to subscribe. 



Some dangerous and mahgnant animals are said (in sober earnest) 

 to wear a perpetual war-paint, in order to "remind their enemies 

 that they had better leave them alonef." The wasp and the hornet, 



* For a more elaborate classification, into colours cryptic, procryptic, anti- 

 cryptic, apatetic, epigamic, sematic, episematic, aposematic, etc., see Poulton's 

 Colours of Animals (Int. Scientific Series, Lxvin, 1890; cf. also R. Meldola, 

 Variable protective colouring in insects, P.Z.S. 1873, pp. 153-162; etc. The subject 

 is well and fully set forth by H. B. Cott, Adaption coloration in Animals, 1940. 



t Dendy, Evolutionary Biology, 1912, p. 336. 



