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PRINCIPLES OF BIOLOGY 
THE PRINCIPLES OF BIOLOGY. 
BY HERBERT SPENCER. 
Exposition of Chapter X.—Genesis, Heredity, and Variation. 
BY W. B. GROVE, B.A. 
This chapter is devoted to the final elaboration of the 
grand doctrine of physiological units (the plastides of some 
authors), by which Herbert Spencer tries to dissipate in some 
degree the mysterious phenomena of Genesis. We may make 
the preliminary remark that the mystery is, and cannot be, 
pay, is not intended to be, completely dissipated ; the 
hypothesis only lends definiteness to our conceptions, and 
enables us to picture faintly to ourselves the mode of action. 
In this respect it resembles that other great doctrine of which 
it is an extension, the atomic theory itself; for after all we do 
not know (perhaps may never know) that atoms really exist; 
they are only mental representatives of something which does 
exist, and which, whatever its nature, obeys the same laws of 
combination and action which we feign for the atoms. It 
amounts to this—that Herbert Spencer’s theory is true in 
fact, if not in form. It reduces the phenomena that we have 
been considering into their places in that vast reign of order, 
the slow, but sure, establishment of which is the object of 
scientific aims. 
These phenomena may be represented in a formula:— 
Genesis — Homogenesis (Gamog.) + Heterog. (Gamog. + Agamog.) 
and we have discovered that the latter part of the formula, 
agamogenesis interrupted by more or less frequently recurring 
gamogenesis, represents the more normal and frequent state 
of things. The question, when gamogenesis recurs, has been 
already answered ; but why ? Let us consider the facts from 
the beginning. 
We suppose '■matter to be built up of atoms, which, by 
their combinations, give rise to molecules. These molecules 
are of gradually increasing complexity. We have the crystal¬ 
loids, composed of few atoms, and comparatively stable ; and 
the colloids, composed of many atoms, and comparatively 
unstable. The modern chemist is familiar with molecules 
consisting of hundreds of atoms, and we have no reason for 
supposing the process to end there. We may reasonably 
imagine these colloidal molecules to unite in molecules of a 
still higher order : these are the physiological units. It is 
known that as the number of unlike, but allied, atoms 
comprising the molecule increases, so in general does its 
