VI PKEFACE. 



observations on their structure, the publication of which 

 led to frequent communications with my late amiable and 

 talented friend, Dr. Johnston, who strongly urged me to 

 commence a more extended systematic investigation of the 

 structural peculiarities of exotic as well as of native species. 

 Thus stimulated, I commenced my investigation of their 

 anatomy, and speedily found in their structure so much 

 that was curious and beautiful, so many admirable mechani- 

 cal and physiological contrivances that I soon became deeply 

 interested in the subject. 



The British sponges alone have afforded me a very exten- 

 sive series of new and beautiful forms of organization, and 

 as my knowledge of the number of the species and the peculi- 

 arities of their structure became extended, I quickly became 

 aware that the list of our native species contained represent- 

 atives of nearly every known genus of these animals, and 

 that such an extension of my investigation as that published 

 in the present volume became absolutely necessary to com- 

 plete the terminology not only of the British species already 

 described, but those also which the future researches of 

 naturalists may make known to us. 



In the pursuit of this object I have done my best to 

 rescue the hidden wonders and beauties of these extraordi- 

 nary creatures from comparative oblivion, and. their exami- 

 nation and investigation have been for more than a quarter 

 of a century a continuous source of fresh pleasures and 

 surprises to me ; but, although in the course of these re- 

 searches I have examined a very large number of exotic as 

 well as of native species, I can assure my readers that I 

 have by no means exhausted the subject, and that a rich 

 field of pleasure still remains to be explored by future 



