viii CONTENTS 



PAGE 



D. Physiology of the Digestive System 139 



E. Blood Vascular System 144 



F. The Excretory System 146 



G. The Muscular System 147 



H. The Nervous System 149 



I. The Reproductive System ....'. 155 



J. Reproduction. Fertilization and Development. 158 



VII. HOMOLOGY AND THE BASIS OF CLASSIFICATION . . ... . . l62 



I. The American Lobster, Homarus Americanus . . . .166 



Appendages and Serial Homolcgy 167 



Digestive System 172 



Blood Vascular System 173 



Excretory System 177 



Muscular System 177 



Nervous System 179 



Sense Organs 179 



Reproductive System 181 



Development and Metamorphosis 182 



II. General Biological Interest of the Lobster 185 



III. Insects 186 



VIII. PARASITISM: PHYSIOLOGICAL ADAPTATION . . . 190 



A. The Tape-worm Taenia sp 190 



B. Animal Associations 193 



C. Adaptations against Parasites 195 



D. The Mechanism of Immunity 199 



IX. THE PERPETUATION OF ADAPTATIONS 203 



A. Animal Descent 204 



B. Evolution 205 



C. Conformity to type 207 



D. Somatic and Germ Plasm 208 



E. The Mendelian Principles of Heredity 219 



A. Heredity of One Pair of Characters 219 



B. Heredity of Two Pairs of Characters 224 



C. Heredity of Sex 225 



F. The Origin of Variations 232 



