XVI PREFACE. 



nised " Ne faites grace a aucune denomination 

 impropre. Ceux qui savent deja, entendront tou- 

 jours; ceux qui ne savent pas encore, entendront 

 plut6t." 



Throughout the whole publication, wherever 

 any fact of importance not depending on their 

 own authority is mentioned, a reference to the 

 source whence it has been derived is generally 

 given ; so that, if the work should have no other 

 value, it will possess that of saving much trouble 

 to future inquirers, by serving as an index to di- 

 rect them in their researches. 



The authors are perfectly sensible that, not- 

 withstanding all their care and pains, many im- 

 perfections will unavoidably remain in their work. 

 There is no science to which the adage, Dies diem 

 docet, is more strikingly applicable than to Natural 

 History. New discoveries are daily made, and 

 will be made it is probable to the end of time ; 

 so that whoever flatters himself that he can pro- 

 duce a perfect work in this department will be 

 miserably disappointed. The utmost that can 

 reasonably be expected from naturalists is to keep 

 pace with the progress of knowledge, and this 

 the authors have used their best diligence to ac- 

 complish. Every new year since they took the 

 subject in hand up to the very time when the first 

 sheets were sent to the press, numerous corrections 



