PROGRESS TOWARDS A NATURAL SYSTEM. 377 



history in detail as examples of mere classification. 

 They will come before us, if at all, more properly 

 when we consider the classifications which depend 

 on the functions of organs, and on the correspond- 

 ing modifications which they necessarily undergo; 

 that is, when we trace the results of physiology. 

 But before we proceed to sketch the history of that 

 part of our knowledge, there are a few points in the 

 progress of zoology, understood as a mere classi- 

 ficatory science, which appear to me sufficiently 

 instructive to make it worth our while to dwell 

 ipon them. 



