CONTENTS xiii 



Supporting Structures 123 



Circulatory System 126 



Alimentary System 126 



VI. ONTOGENESIS 129 



Biogenesis and A biogenesis 130 



Reproduction as a Growth Process . . . .181 



Fission in Metazoa 132 



Fission in Lower Plants . . . . '_ * . 135 

 Temporary Budding . . " . . .136 



Permanent Budding 139 



Spore Formation . . . . ~ . . 140 

 Sexual Reproduction . . . ... . .141 



Total Conjugation 142 



Isogamy . . . 142 



Anisogamy 144 



Sexual Differentiation . . . . .147 



Partial Conjugation 151 



Cytoplasmic Conjugation (Plastogamy) . . 151 



Nuclear Conjugation (Karyogamy) . . . 152 



Nuclear Phenomena of Zygosis in Animals . . 155 



Cleavage 158 



Gastrulation . . . . . . .161 



Further Differentiation . ... 162 



Conjugation in Protozoa 164 



Parthenogenesis 167 



Artificial Parthenogenesis 169 



Alternation of Generations in Animals . . 171 



Sexual Reproduction in Plants .... 174 



Liverworts and Mosses .... 175 



Ferns 176 



Seed Plants 177 



Germination of the Megaspore . . . 179 



Germination of the Microspore . . .179 



Parthenogenesis in Plants .... 182 



Apogamy 183 



The Probable Evolution of the Plant World . .183 



Morphogenesis 185 



Regeneration . . 185 



