110 THE LESSON OF EVOLUTION 



how variations arose. His opinions were wonder- 

 fully shrewd, considering the time at which he 

 worked; and probably all three are correct, so far 

 as they go. But they do not really explain how 

 variations arise. For an organ must be in existence 

 .before it can be used ; and no connection is shewn, 

 between the direct action of physical agencies on 

 plants and the various forms which they have 

 .assumed. Also a very large number of facts are left 

 without any explanation at all. For form does not 

 always change with habit ; as in the fruit-eating 

 bats, the honey-eating bears, and in the carrion 

 crow. While very many changes of form cannot be 

 connected with change of habits. 



The hypothesis of "Organic Polarity " of Spencer; 

 Nageli's "Principle of Perfection"; and Eimer's 

 Orthogenesis are metaphysical conceptions and not 

 scientific. Also they all suppose a necessary pro- 

 gressive principle in the development of protoplasm, 

 which is disposed of by the fact that some low forms 

 of life remained almost unchanged through several 

 geological periods. Nageli explains this by the sup- 

 position of spontaneous generation, which cannot be 

 allowed at the present day. I will give one reason 

 only. There are certain Kadiolarians of the Cam- 

 brian period whose skeleton is so like that of some' 

 now living that all have to be placed into the same 

 genus. Now, although the Radiolarians belong to 

 the Protozoa, they have a very complicated skeleton 

 of very various patterns, and it is impossible to 

 suppose that two quite independent organisms could 

 each originate a highly complex skeleton so similar 



