CONTENTS 



CHAPTER I 



PAGE 



The structure of living matter Unicellular and multicellular animals and 

 plants Life cycles of unicellular animals Reproduction in multi- 

 cellular animals and plants The life cycles of multicellular organisms 

 Theories of einboitement, pangenesis, and idioplasm Experiments 

 bearing upon these theories ........ 1 



CHAPTER II 



Structure of a cell Phenomenon of cell division Selective division of 

 certain parts Theory identifying Niigeli's idioplasm with chromatin 

 Objections The maturation of the gametes The meiotic phase 

 The impossibility of particular characters common to the race being 

 borne by particular chromosomes Fertilisation Parthenogenesis 

 Fertilisation in unicellular animals Experiments in artificial fertilisa- 

 tion and their bearing upon the existence of an hereditary substance 

 Conclusions . . . . ...... 13 



CHAPTER III 



Differentiation of cells Inborn and acquired characters Mental char- 

 acters in man -Physical characters Instinct Lamarck's theory The 

 Darwin-Wallace theory Weismann's theory Oscar Hertwig's theory 



CHAPTER IV 



Variation De Vries' mutation theory The case of (Enothera The dis- 

 appearance of characters Variation in grafts The cell layers in the 

 embryo Variations in wild and domesticated races Arguments 

 against the origin of species per salt um Fertility of hybrids . . 59 



CHAPTER V 



Adaptation Difficulty of explaining by the mutation theory Examples 

 of adaptation Protective coloration Seasonal changes Imitative 

 adaptation Pitcher -plants Drosera The Yucca and the moth Pro- 

 imba Parasitic adaptation The material provided by variation for 

 natural selection to work upon The biome.trical principle Conclusions 77 



CHAPTER VI 



and individual inborn characters Immunity to diseases Malaria 



Measles Tuberculosis Conclusions 102 



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