8 THE THEORY OF [pt. 



to lead, in the minds of those most intimately acquainted with it, to 

 thoughts of a metaphysical character. Nor, it seemed, did those who 

 worked on it do much to diminish its wonder. "Neither the schools 

 of physicians", as Harvey said, "nor Aristotle's discerning brain, 

 have disclosed the manner how the Cock and its seed, doth mint and 

 coine, the chicken out of the Ggg,'^ Or, in the words of Erycius 

 Puteanus, "I will neglect gold, and will praise what is more precious 

 than any metal, I will despise feasts, and will set forth praises of 

 something better than any food or drink. If you would know of what 

 it is that I intend to speak, it is the egg; men marvel at the sun, at 

 meteors flung from heaven, at stars swimming therein, but this is 

 the greatest of all wonders". Here, however, there is one significant 

 thing. It is that the very chapter of Harvey's book in which the 

 preceding remark is found has as its heading "The Efficient Cause 

 of the Chicken, is hard to be found out". It certainly was, but the 

 right clue was in the heading to that exercitation. 



This close association of embryology with philosophy, then, made 

 it necessary to discuss at the outset of this book certain points in the 

 more theoretical regions of biology, and, as it were, to defend from 

 a theoretical angle the extension of the domain of physics and 

 chemistry over embryology. I might have entitled this part of the 

 book "The philosophy of embryology", but, in deference to those 

 metaphysicians who rightly insist that the word philosophy should 

 only be used of a definite system of experience which looks at the 

 universe as a corporate whole, I adopted the present heading. Under 

 it I propose to discuss the exact status of the chemical aspect of 

 embryology. For many biologists, having perhaps insufficiently con- 

 sidered the nature of the scientific method, think it likely that 

 the discoveries of modern times may allow of some other basis for 

 biology than mathematical physics and that the scientific niethod 

 may rightly be different in biology from what it is in chemistry. It 

 is this factor in our present intellectual climate which makes it neces- 

 sary to preface by a philosophical discussion a book in which the 

 concepts of physics and chemistry are extended to a field of biology 

 where they have never before received more than a conventional and 

 formal reverence. 



The aim of all studies in physico-chemical embryology must be 

 that expressed by T. H. Huxley when he said, " Zoological Physiology 

 is the doctrine of the functions or actions of animals. It regards 



