ON GENERATION. 393 



appears that the veins do by no means all proceed from the 

 liver as their origin and commencement, but from the heart 

 unless indeed any one would be hardy enough to contend that 

 a vessel proceeded from its branches, not the branches from the 

 trunk of the vessel. 



Moreover, as the vessels in question are distributed equally 

 to the albumen and vitellus of the egg, not otherwise than as 

 the roots of trees are connected with the ground, it is obvious 

 that both of these substances must serve for the nutriment of 

 the embryo, and that they are taken up and carried to it by 

 these vessels. But this view is opposed to that of Aristotle, 

 who everywhere maintains that the chick is formed from the 

 albumen, and receives nourishment through the umbilicus alone. 

 The albumen indeed is first consumed, and the yelk serves subse- 

 quently for food, supplying the place of the milk, which viviparous 

 animals receive after their birth from their mothers. The food 

 which nature provides for the young of viviparous tribes in the 

 dug of the mother, she supplies in the yelk of the egg to the 

 young of oviparous animals. Whence it happens, that when 

 the albumen is almost wholly consumed, the vitellus still re- 

 mains nearly entire in the egg, the chick being already perfect 

 and complete; more than this, the yelk is still found in the 

 abdomen of the chick long after its exclusion. Aristotle dis- 

 covered some on the eighteenth day after the hatching; and I 

 have myself seen a small quantity connected with the intestine 

 at the end of six weeks from that epoch. 



Nevertheless, from the yelk (which certainly does not de- 

 crease in the same ratio as the albumen whilst the chick is 

 forming) that is taken into the abdomen of the chick, and from 

 the distribution of vessels through its substance, the whole of 

 these collecting into a single trunk which enters the porta of 

 the liver, and doubtless carrying that portion of yelk they have 

 absorbed for more perfect elaboration in that viscus these and 

 other arguments of the like kind force me to say that I cannot 

 do otherwise than admit with Aristotle that the yelk supplies 

 food to the chick, and is analogous to milk. 



The whole of the yelk, indeed, does not remain after the 

 foetus of the fowl is fully formed ; for a certain portion of it has 

 been liquefied on the very first appearance of the embryo, and 

 receives branches of vessels no less than the albumen, by which, 



