NO: 12] ORGANIC VARIATION. 297 
of its organs which had been disturbed by a change of environ- 
ment. Even in the case of a disease attacking an organism, 
may we not regard any abnormal growth produced by the 
afflicted organism itself, to be the structural result of vital 
processes in the organism striving to restore the correlation of 
its organs? Indeed if we consider, which we must in view of 
the facts at hand, that correlation of the organs is a physio- 
logical necessity for the existence of an organism, then, if this 
correlation be disturbed by a change of environment, we are 
logically forced to conclude that the organism must make the 
attempt to restore this correlation, and that structural variations 
would be the result of such a physiological exertion. 
A similar explanation of the origin of structural variations 
can be reached also from another standpoint : when a change 
of environment disturbs the correlation of the organs, the cor- 
relation when restored must differ to some extent from the 
previous state of correlation, since the new environment exerts 
a different influence upon the functional activity of the organs. 
But, as a different state of correlation cannot be conceived as 
existing in the same structural unity, certain changes of struc- 
ture are necessarily involved, and these we term “variations.” 
The statistics given in this paper on variation in birds show 
that species with restricted breeding ranges and which are non- 
migratory in habit are, as a rule, much less variable with regard 
to dimensions — other factors being approximately equal — than 
are species occupying more extensive and more diversified areas, 
and which undertake periodical migrations of considerable mag- 
nitude. We are justified in concluding from these facts, that 
as a rule the amount of variation stands in direct ratio to the 
degree of environmental diversity of the inhabited area, z.e. to 
the amount of change of environment which influences the 
organism. And, as the degree of interruption of the correlation 
of the organs must be in direct proportion to the amount of 
change in the environment, the greater variation in those species 
of extended and diversified habitats is easily and solely explain- 
able on our deduction, that the greater change in the environ- 
ment should cause greater physiological independence between 
the several organs ; and therefore the structural changes ensu- 
