36 NATURE STUDY 



have been thrown into a stream, and carried 

 by the current into a wide lake. The men 

 who are trying to reconstruct the puzzle, 

 do not recover all the pieces at once ; some 

 parts have been lost in their passage to the 

 lake ; others are chipped and altered. These 

 difficulties render the reconstruction of the 

 puzzle an almost impossible task, and so it 

 is in arranging plants and animals. We do 

 not yet know all the species in existence ; 

 some have died out ; others have probably 

 modified their specific characters in the 

 lapse of ages. The consequence is that we 

 have to work with tentative schemes of 

 classification, full of anomalies and ex- 

 ceptions, and liable to constant alteration 

 as our knowledge extends. Such as they 

 are, however, they are indispensable, if we 

 wish to thread our way through the maze 

 of forms which exist in various parts of 

 the globe. 



Much may be learned, and, indeed, must 

 be learned, from books ; but personal observa- 

 tion is at once the most agreeable and the 

 surest mode of acquiring a knowledge of 

 plants and animals. In the course of a few 



