xvi TABLE OF CONTENTS 



LESSON XXI. 



PAGE 



NITELLA 204 



LESSON XXTT. 



HYDRA 219 



LESSON XXITT. 



HYDROID POLYPES 234 



BOUGAINVILLEA, &C 234 



DIPHYES 249 



PORPITA . . 250 



LESSON XXIV. 



SPERMATOGENESIS AND OOGENESIS . . . 252 



THE MATURATION AND IMPREGNATION OF THE OVUM . . . 255 



THE CONNECTION BETWEEN UNICELLULAR AND DIPLOBLASTIC 



ANIMALS 26l 



LESSON XXV. 



POLYGORDIUS 267 



LESSON XXVI. 

 POLYGORDIUS (continued) 289 



LESSON XXVII. 



THE GENERAL CHARACTERS OF THE HIGHER ANIMALS . . . 303 



THE STARFISH 305 



THE CRAYFISH . ^ Io 



\J 



THE MUSSEI .... 316 



THE DOGFISH 



