THE ORIGIN OF LIFE 83 



believe that animals are descended from at most only 

 four or five progenitors, and plants from an equal or lesser 

 number. Analogy would lead me one step further, namely, 

 to the belief that all animals and plants are descended from 

 some one prototype. But analogy may be a deceitful guide. | 



Here similarity of plan and early embryonic 

 similarity are taken as evidence of common ancestry. 

 But this is entirely gratuitous, for the first may repre 

 sent a planning mind following the same ideas in 

 different works ; the second may depend merely on 

 the fact that all ordinary organic development is 

 from the more simple to the more complex. But 

 even if this be granted, the great apostle of evolution 

 still demands four or five primitive species for animals, 

 and about the same for plants. Whence these are to 

 be obtained he cannot tell. Analogy, he says, would 

 lead to one common prototype, but admits that 

 analogy may deceive. It is certain to do so when it 

 proceeds on such data as those he has given ; and 

 even if followed as reliable we have still to ask : 

 Whence, and of what nature, is this prototype, holding 

 within itself the promise and potency of all living 

 things, which are to be unrolled from its almost 

 boundless capacities ? 



The questions we have just been considering have 

 led us to think of those ancient animals whose re 

 mains are preserved in the rocky strata of the earth, 

 and among which, if anywhere, we should find evi 

 dence of the origin of life. I have elsewhere shown 



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