vi Preface 



the question arises: What moulds these independent 

 characters into a harmonious whole? 



The vitalist settles this question by assuming the 

 existence of a pre-established design for each organism 

 and of a guiding '"force" or "principle" which directs 

 the working out of this design. Such assumptions 

 remove the problem of accounting for the harmonious 

 character of the organism from the field of physics or 

 chemistry. The theory of natural selection invokes 

 neither design nor purpose, but it is incomplete since 

 it disregards the physicochemical constitution of living 

 matter about which little was known until recently. 



In this book an attempt is made to show that the 

 unity of the organism is due to the fact that the egg 

 (or rather its cytoplasm) is the future embryo upon 

 which the Mendelian factors in the chromosomes can 

 impress only individual characteristics, probably by 

 giving rise to special hormones and enzymes. We can 

 cause an egg to develop into an organism without a 

 spermatozoon, but apparently we cannot make a sperm- 

 atozoon develop into an organism without the cyto- 

 plasm of an egg, although sperm and egg nucleus 

 transmit equally the Mendelian characters. The con- 

 ception that the cytoplasm of the egg is already the 

 embryo in the rough may be of importance also for the 

 problem of evolution since it suggests the possibility 

 that the genus- and species-heredity are determined by 

 the cytoplasm of the egg, while the Mendelian heredi- 



