CONTENTS 



XV 



PAGE 



Respiratory Organs of Land Animals 100 



The Tracheal System of Insects 101 



Lungs 102 



Respiratory Pigments 102 



Excretion 103 



Excretory Organs of Lower Animals 104 



Kidneys of Higher Animals 105 



Kidneys, Mode of Operation 106 



Section 4. Adjustment of Organisms 



CHAPTER XII 

 How Plants are Adjusted to their Environment 



The Environment 109 



The Necessity for Adjustment 109 



Plants and Animals Contrasted 110 



The Adjustment of Roots to the Soil 110 



Geotropism 1 10 



Chemotropism Ill 



Thermotropism 1 12 



Other Tropisms of Roots 112 



Adjustment of Stems 112 



Tendrils and Twining Stems 113 



Adjustment of Leaves 114 



Adjustment of Reproduction 115 



Internal Correlations in Plants 117 



The Mechanism of Tropisms 117 



The Mechanism of Correlation in Plants . .s. 118 



CHAPTER XIII 



Movement in Animals 



Movement in Protozoa 119 



Amoeboid Motion 119 



Ciliary Motion 119 



Flagellate Motion 120 



Contraction of Protoplasmic Strands 121 



Motion in Many-Celled Animals 121 



Muscles 122 



The Biological Importance of Motion 122 



The Regulation of Motion 124 



Types of Effectors 125 



Skeletal Muscles 125 



Smooth Muscles 125 



Heart Muscle 125 



Muscle Fibers 126 



Make-up of Skeletal Muscle 126 



Make-up of Smooth Muscle and Heart Muscle 127 



The Structure of Skeletal Muscle Fiber 127 



