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Linnaeus, partly under Cuvier, and so on. But the conception of 
evolution cannot, of course, "be classified with either of the sub- 
sciences of form or function, but rather they with it. Evolution 
considers form and function no longer statically, but in movement. 
The line of thought which follows out the conception of evolution 
cannot thus be represented in the above diagram ; it lies in a third 
plane, and must be traced through the pile of accumulated concrete 
facts at right angles. Evolution bears, in fact, the same relation 
to morphology and physiology as history to statistics.* 
§ 3. Application . — The preceding summary, if indeed just and 
accurate, will (a) enable the student to recognise the historic evolu- 
tion in its naturalness and unity, and ( b ) afford a ready and orderly 
method of passing beyond the limits of his own immediate specialty 
towards the unravelment, nay, even the mastery, not indeed of 
the entire quantity, but of the whole essential literature of biology. 
But (c) a yet more important practical result is forcibly suggested 
by this bird’s-eye view. If, as has been shown, morphology and 
physiology have alike found not only a deeper, but an ultimate con- 
tact, in the study of protoplasm, then we have travelled to the very 
limits of empirical research, and, qualitatively speaking, can go no 
further. As Foster suggests, a new departure becomes, however, 
possible. Without, of course, checking the detailed labours of mor- 
phologist and physiologist in developing any of the five inductive 
lines of inquiry, it is now incumbent on the biologist to interpret 
the results deductively in terms of their fundamental secret, nay, 
even to verify them by prediction. It is no longer sufficient to 
accumulate additional empirical detail, however interesting ; what 
has been already gained must also be appreciated and rationalised. 
It is necessary, in short, to retrace the progress of the science, to 
interpret structure and function at all their levels, in terms of pro- 
toplasm, and thus furnish the deductive rationale of each hitherto 
merely empirical order of observed fact and connecting theory. If 
the waves of inductive research have reached their utmost (qualita- 
tive) limit, the possibility of returning on the reverse wave is now 
at least open, great though may be the risks. But a concrete 
example of this is still required. In the author’s recent Encyclo- 
paedia Britannica articles, the phenomena of Reproduction and Sex 
* Cf. the writer’s “Classification of Statistics,” Troc. Roy. Soc. Edin., 1881. 
