194 INTRODUCTION TO ZOOLOGY. 



exploration of this sea exhibited, in regard to depth, a series 

 of phenomena similar to what had been already observed by 

 geologists with regard to successive periods of time, or to de- 

 grees of latitude in geographical distribution; thus showing 

 that the study of the characters which Nature now exhibits 

 furnishes the key to that series of ciphers in which she has 

 written the history of the past. 



It will be seen, therefore, that, in the study of the Testacea, 

 the naturalist rises from the determination of species to 

 inductions which lead him to examine the structure, habits, 

 and distribution of extensive groups; to investigate the con- 

 ditions under which they are found to exist; and, uniting in 

 one series the past and the present, to aim at generalizations 

 sufficient to task, to their utmost capability, the limited 

 powers with which man, in his present state of existence, has 

 been endowed. 



KND OF PART I. 



