1 1 4 DISCRIMINATIONS CHAP. 



presumption is that, as solitary excep- 

 tions are really unknown in Nature, the 

 same processes may very well have been 

 often repeated from time to time. Or 

 perhaps even it may be true that such 

 processes are involved in, and form an 

 essential part of, the infinite mysteries of 

 what we call, and think of so carelessly, 

 as ordinary generation. This is an idea 

 which opens very wide indeed our intel- 

 lectual eyes, and gives them much to do 

 in watching and interpreting the fathom- 

 less wonder of familiar things. 



Let us, however, provisionally at least, 

 accept the belief that organic life was first 

 called into existence in the form of some 

 three, or four, or five germs each being 

 the progenitor of one of the great lead- 

 ing types of the animal creation in 

 respect to peculiarities of structure one 

 for the Vertebrata, one for the Mollusca, 

 one for the Crustacea, one for the 



