FORM DETERMINED BY FUNCTION. 23 



that use after first serving their other function. The sculptured 

 patterns on the scales of reptiles, on the other hand, may be 

 regarded as the transformed and now useless remains of those 

 casting hairs whose utility ended with the preparing the old 

 dead skin for its casting by slightly loosening it; while the 

 remains of others of these casting hairs have grown to be 

 other functional organs — as sensitive hairs and clinging bristles 

 — because they possessed such characters as qualified them 

 for such special functions. Hence we may say that the sculp- 

 tured markings on the scales of those reptiles which cast their 

 skins are no longer to be designated as morphological characters, 

 since it has been shown that they originate by the transforma- 

 tion of parts which have a determinate, highly specialised and 

 indispensable, or at any rate most useful function to perform in 

 the life of the animal. 



This one example may, and in this place must, suffice to 

 show that we need not abandon the hope of explaining mor- 

 phological characters on Darwinian principles, though their 

 nature is no doubt often difficult to understand. If it be 

 granted that it is possible — or if we are at any rate allowed to 

 attempt — to show, that in fact all those hitherto inexplicable and 

 so-called morphological characters have still a determinate func- 

 tion, or have at any time had one. and may be regarded as true 

 or as rudimentary organs which were enabled by their living 

 elements to undergo further transformations and changes of 

 function — if so much as this is hypothetically granted, the 

 direction of our researches is clearly pointed out, and we are 

 justified in prosecuting them. For since we consider all the 

 parts of the animal body as true organs, and see that the sum 

 total of their functional activity determines the vital fitness of 

 the species, we perceive that it is the task of the zoologist to 

 enquire how the conditions of life must act upon individual 

 animals and their organs, in order to be able to deduce our 

 inferences as to the physiological causes of the origin of 

 difierent animal forms. We shall not, however, follow the 

 morphologist, who seeks to trace the affinities which must exist 

 between all living animals by investigating and comparing the 

 forms and organs of living and extinct animals as well as the 



