sorbed and used up sooner than the thick, as if it formed the more appropriate aliment, and were more readily transmuted into the substance of the embryo, of the chick that is to be. The yelk, therefore, appears to be a more distant or ultimate aliment than the albumen, the whole of which has been used up before any notable portion of the vitellus is consumed. The yelk, indeed, is still found inclosed within the abdomen of the chick after its exclusion from the shell, as if it were destined to serve the new being in lieu of milk for its sustenance.
Eggs, consisting of white and yellow, are therefore more perfect, as more distinct in constitution, and elaborated by a higher temperature. For in the egg there must be included, not only the matter of the chick but also its first nutriment ; and what is provided for a perfect animal, must, itself, be per- fect and highly elaborated; as that is, in fact, which consists of different parts, some of which, as already stated, are prior and purer, and so more easy of digestion ; others posterior, and therefore more difficult of transmutation into the substance of the chick. Now the yelk and albumen differ from one another by such kinds of distinction. Perfect eggs are, consequently, of two colours : they consist of albumen and yelk, as if these constituted fluids of easier or more difficult digestion, adapted to the different ages and vigour of the chick.
EXERCISE THE THIRTY-SEVENTH.
Of the manner in which the egg is increased by the albumen.
From the history it appears that the rudiments of the eggs in the ovary are of very small size, mere specks, smaller than millet seeds, white and replete with watery fluid : these specks, however, by and by, become yelks, and then surround them- selves with albumen.
Aristotle seems to think that the albumen is generated in the way of secretion from the vitellus. It may be well to add his words : l " The sex," he says, "is not the cause of the double
1 De Gener. Animal, lib. iii, cap. 1.
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