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ON THE NATURAL FACULTIES Book I
[p. 19] namely, Genesis, Growth, and Nutrition. Genesis, however, is not a simple activity of Nature, but is compounded of alteration and of shaping.
Genesiscorresponds to the intrauterine life, or what we may call embrogeny. Alteration here means histogeness or tissue-production; shaping or moulding (in Greek diaplasis)means the ordering of these tissues into organs (organogenesis).
That is to say, in order that bone, nerve, veins, and all other [tissues] may come into existence, the underlying substance from which the animal springs must be altered; and in order that the substance so altered may acquire its appropriate shape and position, its cavities, outgrowths, attachments, and so forth, it has to undergo a shaping or formative process.
cf. p. 25, note 4.
One would be justified in calling this substance which undergoes alteration the material of the animal, just as wood is the material of a ship, and wax of an image. Growth is an increase and expansion in length, breadth, and thickness of the solid parts of the animal (those which have been subjected to the moulding or shaping process). Nutrition is an addition to these, without expansion.
Let us speak then, in the first place, of Genesis, which, as we have said, results from alteration together with shaping.
The seed having been cast into the womb or into the earth (for there is no difference),
Note inadequate analogy of semen with fertilised seeds of plants (i.e. of gamete with zygote). Strictly speaking, of course, semen corresponds to pollen. cf. p. 130, note 2.
then, after a certain definite period, a great number of parts become constituted in the substance which is being generated; these differ as regards moisture, dryness, coldness and warmth,
ie.the four primary qualities; cf. chap. iii. supra