mediate units, which we may term physiological. There seems no alternative but to suppose that the chemical units combine into units immensely more complex than themselves, complex as they are; and that in each organism, the physiological units produced by this further compounding of highly compound atoms, have a more or less distinctive character. We must conclude that in each case, some slight difference of composition in these units, leading to some slight difference in the mutual play of forces, produces a difference in the form which the aggregate of them assumes ."—Principles of Biology, vol. i. pp. 182–3.
"... the assumption to which we seem driven by the ensemble of the evidence is, that sperm cells and germ cells are essentially nothing more than vehicles, in which are contained small groups of the physiological units in a fit state for obeying their proclivity towards the structural arrangement of the species they belong to."—Ibid. pp. 254–5.
"If the assumption of a special arrangement of parts by an organism is due to the proclivity of its physiological units towards that arrangement, then the assumption of an arrangement of parts slightly different from that of the species, implies physiological units slightly unlike those of the species, and these slightly-unlike physiological units, communicated through the medium of sperm cell or germ cell, will tend, in the offspring, to build themselves into a structure similarly diverging from the average of the species."—Ibid. p. 245.
"The repair of a wasted tissue may therefore be considered as due to forces analogous to those by which a crystal reproduces its lost apex, when placed in a solution like that from which it was formed. In either case, a mass of units of a given kind shows a power of integrating with itself diffused units of the same kind; the only difference being that the organic mass of units arranges the different units into special compound forms, before integrating them with itself.....
