PREFACE. Ul 



The investigation of dates is the most disheartening work 

 upon which the time of an author can be employed ; it is never 

 safe to take them second-hand, and even reference to the origi- 

 nal works is not always satisfactory.* 



Two lists of Errata have been given, and it is earnestly re- 

 commended that these corrections be made with pen and ink at 

 the places indicated. Small and self-evident typographical errors 

 have not been enumerated ; the difficulty of avoiding them, in 

 a treatise of this kind, can only be appreciated by those who 

 have had personal experience. 



Those portions of the work have been treated in most detail 

 which throw light on particular branches of anatomy and physio- 

 logy ; or on great natural-history problems, such as the value of 

 species and genera, and the laws of geographical and geological 

 distribution. It is in these departments that the affinity of 

 natural science to the highest kinds of human knowledge is most 

 distinctly seen ; and in them the richest and noblest results are 

 to be obtained. For to the thoughtful and earnest investigator, 

 nature ever discloses indications of harmony and order, and 

 reflects the attributes of the Maker. 



The recreations of the young seldom fail to exercise a serious 

 influence on after life; and the utility of their pursuits must 

 greatly depend on the spirit in which they are followed. If 

 wisely chosen and conscientiously prosecuted they may help to form 

 habits of exact observation ; they may train the eye and mind to 

 seize upon characteristic facts, and to discern their real import; 

 to discriminate between the essential and the accidental, and to 

 detect the relations of phenomena, however widely separated and 

 apparently unlike. In this way "la belle Science," (as Mr. 

 Gaskoin calls Conchology !) may acquire the influence of pursuits 

 more usually resorted to for mental development and discipline. 



The writer desires again to acknowledge the assistance he 



* The dates on the title pages of Journals and Transactions of Scientific 

 Societies, ai-e not usually dates of pttblicaiion, hntvefev to the years for wkic/t 

 they are issued to the subscribers. It is almost impossible, afterwards, to 

 correct these false dates. 



