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'ZS^HEX I BEGAN THE WRITING OF THIS BOOK, I INTENDED 



merely to set forth my views on some biological problems 

 which I had studied during a period of more than twenty- 

 five years of research on the eggs of marine animals. I had 

 thought my task easy; that it would be a simple matter to 

 present my ideas and findings against the clearly delineated 

 back-drop of general biological theories and on the basis of 

 well-established fact. Merely to hint at the theories and 

 to indicate briefly the factual evidence would suffice, I 

 thought, to make myself clear to my colleagues. But in 

 thinking thus, I had deluded myself; soon I realized that 

 the back-drop had to be cleared in order to show its con- 

 tours; that instead of a substantial platform I had only 

 pieces of material that had first to be ordered and put 

 together before they could serve me. This work had to be 

 done, I found, before I had a stage on which I could present 

 my own ideas and let them speak their parts in my inter- 

 pretation of the drama of life unfolding before our eyes. 

 It thus became imperative for me to examine and to 

 appraise hypothesis and factual evidence and to define first 

 every problem the discussion of which I had projected for 

 my book. 



Thus my book developed from a mere statement of my 

 views for biologists engaged in a narrowly restricted field of 

 investigation into a thoroughgoing presentation and dis- 

 cussion of biological problems for a wider audience. To all 

 those who look with interest upon the manifestations of life 

 in animals and in man, who desire to know more, and more 



vii 



