( Ixxvii ) 



internal differences incapable of being estimated by our 

 present methods.* 



From these considerations another step brings us back to 

 physiological correlation. If variability of nervous function 

 can be seized upon by natural selection, it is but reasonable 

 to suggest that variability of other internal functions can also 

 be utilised when of advantage. Of the functions discharged 

 by the internal organs other than the nervous system, all 

 those obscure chemical processes concerned with metabolism 

 and nutrition, waste and repair, secretion and excretion, and 

 so forth, must be in adjustment with the life conditions of the 

 organism. If species are adapted to their mode of existence, 

 as is admitted by all schools of evolutionists, f the selectionist 

 must explain the physiological adaptation in the same way 

 that he explains the structural adaptation, viz., by the sur- 

 vival of individuals whose physiological processes are best in 

 harmony with their mode of life. But this explanation starts 

 from a variability of physiological function, and here I con- 

 fess that systematic observation is sadly wanting. Considering, 

 however, how much practical difficulty surrounds the investi- 

 gation of the physiology of any one organ, even in the higher 

 animals, it is by no means surprising that the question of 

 functional variability of this kind should not hitherto have 

 received the same attention from physiologists that the more 

 obvious structural variability has received from the morpholo- 

 gists. From analogy with the known variability of structure 

 it is fair to infer that a physiological variability also exists, 



* " What student of the animal kingdom is ignorant of the deep correla- 

 tion existing between seemingly immaterial outward characters and import- 

 ant points in internal organisation, so that artiticial systems built on the 

 former alone nevertheless result in a grouping quite coiTCsponding to natural 

 relationships?" — From a lecture on "Zoology since Darwin," by Prof. 

 Ludwig von Graff, " Natural Science," Vol. IX., p. 36(3. 



+ '' Not only do specific forms exist in nature, but they exist in such a way 

 as to fit the place in Nature in which they are placed ; that is to say, the 

 specific form which an organism has, is iidapted to the position which it fills 

 . . . the adaptation is not absolute." — Bateson's "Materials for the 

 Study of Variation," p. 3. "Darwin's 'survival of the fittest' we may 

 alone regard as absolutely demonstrated as a real factor, without committing 

 ourselves as to the "origin of fitness.' " — From the fifth (Prof. H. F. Osborn's 

 biological lecture, delivered at the Marine Biological Laboratory of Wood's 

 Holl; Boston, 189.5. 



