colour, as if the white were derived from the male, the yellow from the female ; both are furnished by the female. But one of them is hot, the other is cold. Now these two portions are distinct in animals, fraught with much heat ; in those that are not so fraught the eggs are not thus distinct. And this is the reason why the conceptions of these are of one colour. But the semen of the male alone sets the conception ; therefore is the conception of the bird small and white in the first instance ; but in the course of time, and when there is a larger infusion of blood, it becomes entirely yellow ; and, last of all, when the heat declines, the white portion, as a humour of equal tem- perature surrounds it on every side. For the white por- tion of the egg is, by its nature, moist, and includes animal heat in itself; and it is for this reason that it is seen in the circumference, the yellow and earthy portion remaining in the interior."
Fabricius, 1 however, thinks that " the albumen only adheres to the vitellus by juxtaposition. For while the yelk is rolled through the second uterus and gradually descends, it also gra- dually assumes to itself the albumen which is there produced, and made ready, that it may be applied to the yelk ; until the yelk having passed the middle spirals and reached the last of them, already surrounded with the albumen, it now surrounds itself with the membranes and shell/' Fabricius will there- fore have it that the egg increases in a two-fold manner : " partly by means of the veins, as concerns the vitellus, and partly by an appositive increase, as regards the albumen." And, among other reasons, this was perchance one for the above opinion : that when an egg is boiled hard the albumen is readily split into layers lying one over another. But this also occurs to the yelk still connected with the ovary, when boiled hard.
Wherefore, taught by experience, I rather incline to the opinion of Aristotle ; for the albumen is not merely perceived as added in the way Fabricius will have it, but fashioned also, distinguished by chalazse and membranes, and divided into two different portions ; and all this in virtue of the inherence of the same vegetative vital principle by which the egg is more conspicuously divided into two distinct substances a yelk and
1 Op. cit. p. 12.
