INO Ie ORGANIC VARIATION. 301 
Therefore, in order to explain the presence of variation in a 
certain species of a group not present in the same organ of 
closely allied species, we must compare the conditions of the 
environment of the one with those of the others. Thus, 
regarded from this standpoint alone, when variation is per- 
ceptible in organ x of species A, but not so in organ + of a 
closely related species 4, we may conclude that organ x of 
species A is being influenced by some change of environment 
which is not affecting the corresponding organ x of species B. 
May we not consider that the particular organ in A is com- 
mencing to develop in a new direction, while the organ in B is 
remaining unchanged? By this would be merely shown, how- 
ever, that whenever variation is noticeable, the organ evincing 
it is tending towards an ultimate structural modification, due to 
the fact of a change of environment already taking, or having 
taken, place. 
What light can the phenomena of variation throw upon the 
phylogeny of organisms? I consider that it may be possible 
to decide, with a certain degree of certainty, whether a given 
species is developing progressively or regressively at the present 
time, and whether in the near past it has progressed or degener- 
ated; by basing our conclusions as to its course of development, 
present and past, upon the direction and degree in which the 
variation appears. This may seem to bea bold assumption, but 
if the views expressed in this paper upon the nature and origin 
of variation be probable, we may yet learn that the study of 
variation may furnish valuable criteria for estimating the facts 
of phylogeny. As Bateson observes (/.c., p. 6), two criteria of 
phylogeny upon which much confidence is misplaced, namely 
the ontogeny and the direct study of adaptation, are by no 
means infallible ; so that to-day we have only the criterion of 
the facts of paleontology, —a criterion which Bateson fails to 
mention, with which we may feel ourselves secure. And this 
being the case, we should gladly avail ourselves of a further 
criterion, namely, the phenomena of variation. 
In comparing the antagonistic states, progressive and regres- 
sive development (cf. Section I), it was found that progressive 
development leads towards a more complicated structural modi- 
