142 TRANSACTIONS OF THE [MAR. 9, 
the constitution, or stirp, had also changed. Illustrations might 
be given of changes of the most profound character induced by 
changes in either of the above factors of environment, and in 
the case of the motor factor or animal motion the habits of the 
animal would, in the course of a life time, profoundly modify its 
structure. For example, if the human infant were brought up 
in the branches of a tree as an arboreal type instead of as a ter- 
restrial, bi-pedal type, there is little doubt that some of the well 
known early adaptations to arboreal habit (such as the turning 
in of the soles of the feet, and the grasping of the hands) might — 
be retained and cultivated; thus a profoundly different type of 
man would be produced. Similar changes in the action of en- 
vironment are constantly in progress in nature, since there is no 
doubt that the changes of environment and the habits which it 
so brings about far outstrip all changes in constitution. This 
fact, which has not been sufficiently emphasized before, offers an 
explanation of the evidence advanced by Cope and other writers 
that change in the forms of the skeletons of the vertebrates first 
appears in ontogeny and subsequentlyin phylogeny. During the 
enormously long period of time in which habits induce onto- 
genic variations it is possible for natural selection to work very 
slowly and gradually upon predispositions to useful correlated 
variations, and thus what are primarily ontogenic variations be- 
come slowly apparent as phylogenic variations or congenital 
characters of the race. Man, for instance, has been upon the 
earth perhaps seventy thousand years; natural selection has 
been slowly operating upon certain of these predispositions, but 
has not yet eliminated those traces of the human arboreal habits, 
nor completely adapted the human frame to the upright posi- 
tion. This is as much an expression of habit and ontogenic 
variation as it is a constitutional character. Very similar views 
were expressed to the speaker in a conversation recently held 
with Professor Lloyd Morgan, and it appears as if a similar con- 
clusion had been arrived at independently. Professor Morgan 
believed that this explanation could be applied to all cases of 
adaptive modification, but it is evident that this cannot be so, 
because the teeth also undergo the same progressively adaptive 
