PAGE 

 206 



xvi TABLE OF CONTENTS 



LESSON XXI. 



NITELLA ................... 



LESSON XXII. 



HYDRA ......... 221 



LESSON XXIII. 



HYDROID POLYPES ........ 2 37 



BOUGAINVILLEA, &C ....... ... 237 



DIPHYES ........ 250 



PORPITA . . 



LESSON XXIV. 



SPERMATOGENESIS AND OOGENESIS .... 255 



THE MATURATION AND IMPREGNATION OF THE OVUM . . 259 

 THE CONNECTION BETWEEN UNICELLULAR AND DIPLOBLASTIC 



ANIMALS .................. 2 64 



LESSON XXV. 



POLYGORDIUS ........... 271 



LESSON XXVI. 



POLYGORDIUS (continued} ................ 293 



LESSON XXVII. 



I HE GENERAL CHARACTERS OF THE HIGHER ANIMALS . . . 307 



THE STARFISH ................... 39 



THE CRAYFISH . . 3 X 4 



THE FRESH-WATER MUSSEL ............. 32O 



I UK DOGFISH . ...... 324 



