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 httle. Nevertheless they are so important, so full of 

 deep theoretical significance, and are so bound up with the general 

 question of form and of its determination as a result of growth, 

 that ^n essay on growth and form is bound to take account of 

 them, however imperfectly 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 demon- 

 stration. With regard to colouration, for instance, it is by colours 

 ''cryptic," "warning," "signalhng," "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 beliefs and doctrines to which it becomes more and more 

 difficult to subscribe. 



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

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

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

 Variable Protective Colouring in Insects, P.Z.S. 1873, pp. 153-162, etc. 



