58 EMBRYOLOGY IN ANTIQUITY [pt. ii 



to say about them." We see here as clearly as possible the beginnings 

 of systematic embryological knowledge, and from this point onwards, 

 through Aristotle, Leonardo, Harvey and von Baer, to the current 

 number of the Archivf. Entwicklungsmechanik, the line runs as straight 

 as Watling Street. 



In Section 30 there is an important passage in which the author 

 discusses the phenomena of birth. "I say", he says, "that it is the 

 lack of food which leads to birth, unless any violence has been done; 

 the proof of which is this ; — the bird is formed thus from the yolk 

 of the egg, the egg gets hot under the sitting hen and that which is 

 inside is put into movement. Heated, that which is inside begins to 

 have breath and draws by counter-attraction another cold breath 

 coming from the outside air and traversing the egg, for the egg is 

 soft enough to allow a sufficient quantity of respiration to penetrate 

 to the contents. The bird grows inside the egg and articulates itself 

 exactly like the child, as I have previously described. It comes from 

 the yolk but it has its food from, and its growth in, the white. To 

 convince oneself of this it is only necessary to observe it attentively. 

 When there is no more food for the young one in the egg and it has 

 nothing on which to live, it makes violent movements, searches for 

 food, and breaks the membranes. The mother, perceiving that the 

 embryo is vigorously moving, smashes the shell. This occurs after 

 20 days. It is evident that this is how things happen, for when the 

 mother breaks the shell there is only an insignificant quantity of 

 liquid in it. All has been consumed by the foetus. In just the same 

 way, when the child has grown big and the mother cannot continue 

 to provide him with enough nourishment, he becomes agitated, 

 breaks through the membranes and incontinently passes out into the 

 external world free from any bonds. In the same way among beasts 

 and savage animals birth occurs at a time fixed for each species 

 without overshooting it, for necessarily in each case there must be 

 a point at which intra-uterine nourishment will become inadequate. 

 Those which have least food for the foetus come quickest to birth 

 and vice versa. That is all that I had to say upon this subject." 



The theory underlying this passage evidently is that the main food 

 of the fowl embryo is the white and that the yolk is there purely for 

 constructional purposes. Had the author not been strongly attached 

 to this erroneous view he could not have failed to notice the un- 

 absorbed yolk-sac which still protrudes from the abdomen of the 



