CONTENTS. 



PAGE 



Preface to the Geiinan Version . . . . .1 



CHAPTER I. 



Tlie development of the Medusae {Scyphistoma-strohila, Medusce), tab. I. 



figs. 1 to 40 11 



CHAPTER II. 



The development of the Claviform Polypes {Corym, Syncoryne, Cory- 



morpha, Campanularia,) tab. I. figs. 41-57 . . .26 



CHAPTER III. 

 The alternate generation of the Salpse {Proles gregata, Proles solitarui) 38 



CHAPTER IV. 



The development of the Trematoda . . . . .52 



(a) Cercaria echinata ? (Siebold) tab. II. . . . .53 



{h) Cercaria armata (Siebold) tab. III. fig. 1-6 . . .74 



ip) Cercaria ephemera (Nitzsch), and Distoma duplicatum (Baer) . 87 



{d) The development of other Trematode animals . . .94 



CHAPTER V. 

 Concluding remarks on the alternating generations and their real nature 105 



EXPLANATION OF THE FIGURES. 



Plate I, The development of the Medusa a^irita . , .117 



II, The development of the Eluke, Z*2s^o»?» jo«cj/?<?« . .124 



III, The development of the Distoma tarda . . .128 



Gnriffendum. — p. 20, I, 16, for generically divided, read of distinct sexes. 



