CONTENTS 



PAGE 



CHAPTER I. Introduction 1 



Scope of work. Heritage and environment. Life: 

 vitalistic and mechanistic concepts. Necessity of mech- 

 anistic point of view in scientific inquiry. Environment 

 as initial source of change. Present autonomy of heritage. 

 Complexity of environment. Direction of inquiry. 



CHAPTER II. Individuals and Species . . 26 



The species problem. Nature of species as a unit. 



Species and evolution. Heritage and environment in 



species and individuals. Individual characters and the 

 characters of species. 



CHAPTER III. Sources of Change . . .47 



Materials and forces in natural entities. Internal and 

 external forces. Change of environment. Fluctuations of 

 heritage. Scientific attitude toward variation: Darwin, 

 Lamarck, Bateson. Osborn's tetrakinetic theory. Modi- 

 fications, recombinations, and mutations. Adaptation: 

 process and result. Adaptability a fundamental property 

 of protoplasm. Mutilations. Fundamental similarity of 

 all acquired characters. Individual characters a part of 

 species complex. Difference between modifications and 

 hereditary characters. Adaptation of species. Selection. 

 Permanence of modifications. Cause of mutations. 



CHAPTER IV. Genetics 76 



Basic concepts of genetics. Chromosomes, nucleus, and 

 cytoplasm in heredity. Action of genes. Cytoplasmic in- 

 heritance. Germ plasm and soma. The body as environ- 

 ment. Relations of body and external environment. En- 

 vironment and germ cells. Stability of genes. Modern 



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