Vlll PREFACE. 



Daly ell, and Agassiz, on the " alternation of generations" among 

 the Hydriform Polyps and Acalephse, promise results of the 

 utmost interest to the Naturalist. 



The discoveries of Milne-Edwards have importantly increased 

 our information concerning the organization of the Mollusca as 

 well as of the Alcyonoid Polyps ; and those of Muller, revealing 

 the metamorphoses of the Echinodermata, add new lustre to a 

 name already so distinguished in science. 



To particularize our own countrymen and fellow-labourers 

 whose names give value to the following pages would be an in- 

 vidious task ; suffice it to say that the Author has endeavoured, 

 to the best of his ability, to keep pace with their diligence and 

 onward progress, so as adequately to record and acknowledge 

 their contributions to the general stock of scientific lore. 



To Mr. Van Voorst, the liberal Publisher of the present 

 volume, the Author cannot but offer his best thanks ; the nu- 

 merous and costly illustrations that adorn the work speak for 

 themselves, while his endeavours to publish it at a price placing 

 it within the reach of every student will, it is hoped, be exten- 

 sively appreciated. 



