much as in both there is accession of new aliment, apposition, agglutination, and transmutation of particles. Nor can vetches or beans, when they attract moisture from the earth through their skins, imbibing it like sponges, be said with less propriety to be nourished than if they had obtained the needful moisture through the mouths of veins ; and trees, when they absorb the dew and the rain through their bark, are as truly nourished as when they pump them in by their roots. With reference to the mode in which nutrition is effected, we have set down much in another place. It is another difficulty that occupies us at this time, viz., whether the yelk, whilst it is acquiring the white, does not make a certain separation and distinction in it ; whether, in the course of the increase, a more earthy portion does not subside into the yelk or middle of the egg as towards the centre, which Aristotle believed, and another lighter portion sur- rounds this. For between the yelk which is still in the cluster, and the yelk which is found in the middle of a perfect egg, there is this principal difference, that although the former be of a yellow colour, still, in point of consistence, it rather resembles the white ; and by boiling, it is, like the latter, thickened, com- pacted, inspissated, and becomes divisible into layers; whilst the yelk of the perfect egg is rendered friable by boiling, and is rather of an earthy consistency, not thick and gelatinous like albumen.
EXERCISE THE ELEVENTH.
Of the covering or shell of the egg.
It will now be proper, having spoken of the production of eggs, to treat of their parts and diversities. " An egg/' says Fabricius, " consists of a yelk, the albumen, two chalazre, three membranes, viz. one proper to the vitellus, two common to the entire egg, and a shell. To these two others are to be added, which, however, cannot be correctly reckoned among the parts of an egg; one of these is a small cavity in the blunt end of the egg, under the shell ; the other is a very small white spot, a kind of round cicatricula connected with the surface of the yelk. The history of each of these parts and accidents must
