xvi TABLE OF CONTENTS 



LESSON XXL 



PAGE 

 HYDRA ......................... 2l8 



LESSON XXII. 



HYDROID POLYPES .................... 234 



BOUGAINVILLEA, &C .................. 234 



DIPHYES ...................... 248 



PORPITA ........ .............. 249 



LESSON XXIII. 



SPERMATOGENESIS AND OOGENESIS . . .......... 253 



THE MATURATION AND IMPREGNATION OF THE OVUM .... 258 



THE CONNECTION BETWEEN UNICELLULAR AND DIPLOBLASTIC 



ANIMALS ...................... 26l 



LESSON XXIV. 



POLYGORDIUS ...................... 268 



LESSON XXV. 

 POLYGORDIUS (continued) ................. 290 



LESSON XXVI. 



THE CHIEF DIVISIONS OF THE ANIMAL KINGDOM ....... 304 



THE STARFISH ...................... 306 



LESSON XXVII. 



THE CRAYFISH ...................... 3 T ^ 



LESSON XXVIII. 



THE FRESH-WATER MUSSEL 



