vni ANIMAL LIFE 



ment, 84. The laws or general facts of development, 86. The 

 significance of the facts of development, 89. Metamorphosis, 

 90. Metamorphosis among insects, 90. Metamorphosis of the 

 toad, 94. Metamorphosis among other animals, 96. Duration of 

 life, 101. Death, 103. 



VI. THE PRIMARY CONDITIONS OF ANIMAL LIFE .... 106 



Primary conditions and special conditions, 106. Food, 106. 

 Oxygen, 107. Temperature, pressure, and other conditions, 108. 

 Difference between animals and plants, 111. Living organic 

 matter and inorganic matter, 112. 



VII. THE CROWD OF ANIMALS AND THE STRUGGLE FOR EXIST- 

 ENCE 114 



The crowd of animals, 114. The struggle for existence, 116. 

 Selection by Nature, 117. Adjustment to surroundings a re- 

 sult of natural selection, 120. Artificial selection, 120. Depend- 

 ence of species on species, 121. 



VIII. ADAPTATIONS 133 



Origin of adaptations, 123. Classification of adaptations, 123. 

 Adaptations for securing food, 125. Adaptations for self-de- 

 fense, 128. Adaptations for rivalry, 135. Adaptations for the 

 defense of the young, 137. Adaptations concerned with sur- 

 roundings in life, 143. Degree of structural change in adapta- 

 tions, 146. Vestigial organs, 147. 



IX. ANIMAL COMMUNITIES AND SOCIAL LIFE .... 149 



Man not the only social animal, 149. The honey-bee, 149. 

 The ants, 155. Other communal insects, 158. Gregariousness 

 and mutual aid, 163. Division of labor and basis of communal 

 life, 168. Advantages of communal life, 170. 



X. COMMENSALISM AND SYMBIOSIS 172 



Association between animals of different species, 172. Com- 

 mensalism, 173. Symbiosis, 175. 



XI. PARASITISM AND DEGENERATION 179 



Relation "f parasite and host, 179. Kinds of parasitism, 180. 

 The simple structure of parasites, 181. Gregarina, 182. The 

 tape-worm and other flat-worms, 183. Trichina and other round- 

 worms, 184. Sacculina, 187. Parasitic insects, 188. Parasitic 

 vertebrates, 193. Degeneration through quiescence, 193. De- 

 generation through other causes, 197. Immediate causes of de- 

 generation, 198. Advantages and disadvantages of parasitism 

 and degeneration, 198. Human degeneration, 200. 



