CLASSIFICATION. 55 



ovarian stage of the invertebrata, and to more advanced stages 

 of the chisses formed upon its own type. And so also with the 

 highest organized mollusca ; after their first stage they resemble 

 the simpler orders of their own sub-kingdom, but not those of 

 any other group. 



These are the views of Professor Owen — the successor of 

 Hunter — by whom it has been most clearly shewn and stead- 

 fastly maintained, that the " unity of organization" manifested 

 by the animal world results from the design of a Supreme 

 Intelligence, and cannot be ascribed to the operation of a me- 

 chanical "law." 



Chapter V. 

 CLASSIFICATION. 



The objects of classification are, frst, the convenient and intel- 

 ligible arrangement of the species ; * and, secondly, to afford a 

 summary, or condensed exposition, of aU that is known respect- 

 ing their structure and relations. 



In studying the shell -fish, we find resemblances of two 

 kinds. First, agreements of structure, form, and habits ; and, 

 secondly, resemblances of form and habits without agreement of 

 structure. The first are termed relations of affinity; the second 

 of analogy. 



Affinities may be near, or remote. There is some amount of 

 affinity common to all animals ; but, like relationships amongst 

 men, they are recognized only when tolerably close. Resem- 

 blances of structure which subsist from a very early age are pre- 

 sumed to imply original relationship ; they have been termed 



* At least 12,000 recent, and 15,000 fossil species of molluscous animals 

 are known. 



