8 REPOET 1893. 



riddle whicli lies outside of our scope. No seriously-minded person, 

 however, doubts tliat organised nature as it now presents itself to us 

 has become what it is by a process of gradual perfecting or advance- 

 ment, brought about by the elimination of those organisms which failed 

 to obey the fundamental principle of adaptation which Treviranus indi- 

 cated. Each step, therefore, in this evolution is a reaction to external 

 influences, the motive of which is essentially the same as that by which 

 from moment to moment the organism governs itself. And the whole 

 process is a necessary outcome of the fact that those organisms are most 

 prosperous which look best after theu' own welfare. As in that part of 

 biology which deals with the internal relations of the organism, the 

 interest of the individual is in like manner the sole motive by which 

 every energy is guided. We may take what Treviranus called selfish 

 adaptation — ZweckmdssigTieit filr sich selher — as a connecting link 

 between the two branches of biological study. Out of this relation 

 springs another which I need not say was not recognised until after the 

 Darwinian epoch — that, I mean, which subsists between the two evolu- 

 tions, that of the race and that of the individual. Treviranus, no less 

 distinctly than his great contemporary Lamarck, was well aware that 

 the affinities of plants and animals must be estimated according to their 

 developmental value, and consequently that classification must be founded 

 on development ; but it occurred to no one what the real link was between 

 descent and develojDment ; nor was it, indeed, until several years after the 

 publication of the ' Origin ' that Haeckel enunciated that ' biogenetic 

 law ' according to which the development of any individual organism is 

 but a memory, a recapitulation by the individual of the development of 

 the race — of the process for which Fritz Miiller had coined the excellent 

 word ' phylogenesis ' ; and that each stage of the former is but a transitory 

 reappearance of a bygone epoch in its ancestral history. If, therefore, 

 we are right in regarding ontogenesis as dependent on phylogenesis, the 

 origin of the former must correspond with that of the latter ; that is, 

 on the power which the race or the organism at every stage of its 

 existence possesses of profiting by every condition or circumstance for its 

 own advancement. 



From the short summary of the connection between different parts of 

 our science you will see that biology naturally falls into three divisions, 

 and these are even more sharply distinguished by their methods than by 

 their subjects ; namely, Physiology, of which the methods are entirely 

 experimental ; Morphology, the science which deals with the forms and 

 structure of plants and animals, and of which it may be said that the 

 body is anatomy, the soul, development ; and finally CEcologij, which uses 

 all the knowledge it can obtain from the other two, but chiefly rests on 

 the exploration of the endless varied phenomena of animal and plant life 

 as they manifest themselves under natural conditions. This last branch 

 of biology — the science which concerns itself with the external relations of 



