"That other kind of repair which shows itself in the regeneration of lost members, is comprehensible only as an effect of actions like those referred to. The ability of an organism to recomplete itself when one of its parts has been cut off, is of the same order as the ability of an injured crystal to recomplete itself. In either case, the newly-assimilated matter is so deposited as to restore the original outline. And if, in the case of the crystal, we say that the whole aggregate exerts over its parts a force which constrains the newly-integrated atoms to take a certain definite form, we must in the case of the organism assume an analogous force."—Ibid. vol. i. pp. 178–9.
"... We must infer that a plant or animal of any species is made up of special units, in all of which there dwells the intrinsic aptitudes to aggregate into the form of that species; just as in the atoms of a salt there dwells the intrinsic aptitude to crystallize in a particular way."—Ibid. p. 181.
"Setting out with these physiological units, the existence of which various organic phenomena compel us to recognize, and the production of which the general law of Evolution thus leads us to anticipate; we get an insight into the phenomena of Genesis, Heredity, and Variation. If each organism is built of certain of these highly-plastic units peculiar to its species—units which slowly work towards an equilibrium of their complex polarities, in producing an aggregate of the specific structure, and which are at the same time slowly modifiable by the reaction of this aggregate—we see why the multiplication of organisms proceeds in the several ways, and with the various results, which naturalists have observed.
"Heredity, as shown not only in the repetition of the specific structure, but in the repetition of ancestral deviation from it, becomes a matter of course; and it falls into unison with the fact that, in various simple organisms, lost parts can be replaced, and that, in still simpler organisms, a fragment can develop into a whole."—Ibid. pp. 287–8.
