Conclusion 255 
think, to have been formed on the same principle as the 
boughs which represent genera, and the twigs which stand 
for species and varieties. If specific differences arise mainly 
from differences of action taken in consequence of differ- 
ences of opinion, then, so ultimately do generic ; so, there- 
fore, again, do differences between families ; so therefore, 
by analogy, should that greatest of differences in virtue of 
which the world of life is mainly animal, or vegetable. In 
this last case as much as in that of specific difference, we 
ought to find divergent form the embodiment and organic 
expression of divergent opinion. Form is mind made 
manifest in flesh through action: shades of mental dif- 
ference being expressed in shades of physical difference, 
while broad fundamental differences of opinion are ex- 
pressed in broad fundamental differences of bodily shape. 
Or to put it thus :— 
If form and habit be regarded as functionally interde- 
pendent, that is to say, if neither form nor habit can vary 
without corresponding variation in the other, and if habit 
and opinion concerning advantage are also functionally 
interdependent, it follows self-evidently that form and 
opinion concerning advantage (and hence form and cun- 
ning) will be functionally interdependent also, and that 
there can be no great modification of the one without 
corresponding modification of the other. Let there, then, 
be a point in respect of which opinion might be early and 
easily divided—a point in respect of which two courses 
involving different lines of action presented equally- 
balanced advantages—and there would be an early sub- 
division of primordial life, according as the one view or the 
other was taken. 
It is obvious that the pros and cons for either course 
must be supposed very nearly equal, otherwise the course 
which presented the fewest advantages would be attended 
with the probable gradual extinction of the organised 
beings that adopted it, but there being supposed two 
