vi CONTENTS 



CHAPTER 



PAGE 



C. Internal Structure 133 



D. Physiology of the Digestive System 136 



E. Blood Vascular System 141 



F. The Excretory System 142 



G. The Muscular System 144 



H. The Nervous System 145 



I. The Reproductive System -, 151 



J. Reproduction. Fertilization and Development . 154 



VII. HOMOLOGY AND THE BASIS OF CLASSIFICATION 158 



I. The American Lobster, Homarus Americanus . . . .162 



Appendages and Serial Homology . . 163 



Digestive System 168 



Blood Vascular System 169 



Excretory System 173 



Muscular System 173 



Nervous System 175 



Sense Organs 175 



Reproductive System 177 



Development and Metamorphosis 178 



II. General Biological Interest of the Lobster 181 



III. Insects 182 



VIII. PARASITISM: PHYSIOLOGICAL ADAPTATION 186 



A. The Tape- worm Taenia sp 186 



B. Animal Associations 189 



C. Adaptations against Parasites 191 



D. The Mechanism of Immunity 195 



IX. THE PERPETUATION OF ADAPTATIONS. 198 



A. Animal Descent . 199 



B. Evolution 200 



C. Conformity to type 202 



D. Somatic and Germ Plasm 203 



E. The Mendelian Principles of Heredity 214 



A. Heredity of One Pair of Characters 214 



B. Heredity of Two Pairs of Characters 219 



C. Heredity of Sex 220 



F. The Origin of Variations 227 



