204 ON GENERATION. 



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 



