306 ON GENERATION. 



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. 



