All Life from the Egg 123 



like the smallest marble in the magic nest of boxes. Once 

 the implications of this doctrine of " encasement " became 

 clear, it became also extremely improbable. Steadily it gave 

 way to the opposite idea: The individual develops from 

 the tgg, gradually taking form by a process of growth 

 and elaboration: the creation of new parts from different 

 structures. 



All Life from the Egg 



Aristotle made an attempt to answer the question of 

 individual becoming by examining on successive days eggs 

 that were being hatched. Lacking a microscope and other 

 accessories of modern investigation, he was limited in what 

 he could observe. He was able to find the pulsating blood 

 vessel in the young embryo but falsely concluded that the 

 heart is the seat of the soul. The logic is perfect, although 

 he was uninformed as to the facts and perhaps confused as 

 to his assumptions. If we assume that the soul (whatever 

 we may think of it) is the essence of life, and if we assume 

 that motion is the essential manifestation of life, it is per- 

 fectly logical to locate the soul in the heart, for it is the 

 heart that shows the first signs of life — that is, movement. 



There was not much progress made in the observation 

 of the chick's development until the Seventeenth Century. 

 Then there became available both better instruments and a 

 new point of view which directed men's attention to facts 

 and placed speculation, as a means of understanding the 

 world, in a subordinate position. The accumulation of ob- 

 servations, the detailed description of egg embryos at suc- 

 cessive stages, the reexamination of what was actually known, 

 led to the conclusion that all life comes from the egg. 



William Harvey, who discovered the circulation of the 

 blood, published later a collection of observations and re- 

 flections on the generation of animals. On the title page of 

 this book Jove is represented opening a sphere from which 

 emerge various kinds of animals, including the human form. 



