44 LIFE ON THE EARTH. 



These gradations and modifications of the parts 

 constituting a general type may be represented by 

 one of three suppositions : First, that the structure 

 is what we see because that portion of the general 

 type, and that state of the organ or constituent part 

 of the type was selected as suitable for the life of the 

 creature; Secondly, that the structure has become 

 what it is by degradation from a fuller type through 

 the reduction or suppression of certain parts by want 

 of exercise of their functions; Thirdly, that the 

 typical structure is incompletely manifested because 

 some of the functions have been unexercised, and 

 the organs which belong to them consequently re- 

 main undeveloped. 



Each of these views may be thought to be so far 

 founded on observation of nature as to be allowed in 

 an hypothesis for comparison with more observations. 

 The choice between them can only be justified by 

 reference to phenomena, which by their number, 

 consistency and critical character, may furnish a basis 

 for sound judgment. Without such reference a 

 choice no doubt will be often made, but it can then 

 be little better than prejudice, and must be expected 

 to differ in different persons, according to the pre- 

 vious training of their minds. It is consoling to 

 believe that each may be connected, indeed will be 

 connected, by minds accustomed 



