PKEFACE TO THE PEE SENT EDITION. 



In preparing a new edition of this Work for the press, 

 every page has passed under the Author's eye, and 

 has been examined with earnest care. A very large 

 portion of it consisting of his own original re- 

 searches, there was little room for alteration ; but 

 new facts, interesting in themselves, and germane to 

 the subjects herein treated, which have been recorded 

 since, he has used to enrich the work. These have 

 been uniformly added in the shape of marginal 

 notes; leaving the text untouched, a reflection of 

 Microscopical Science fifteen years ago. 



P. H. G. 



Torquay, Jan. 1874. 



