378 THE CAUSES OF THE xi 



which is also a crustacean. So that you have all 

 the Fauna reduced, at this period, to four forms : 

 one a kind of animal or plant that we know no- 

 thing about, and three undoubted animals two 

 crustaceans and one mollusc. 



I think, considering the organisation of these 

 mollusca and Crustacea, and looking at their very 

 complex nature, that it does indeed require a very 

 strong imagination to conceive that these were the 

 first created of all living things. And you must 

 take into consideration the fact that we have not 

 the slightest proof that these which we call the 

 oldest beds are really so : I repeat, we have not 

 the slightest proof of it. When you find in some 

 places that in an enormous thickness of rocks 

 there are but very scanty traces of life, or abso- 

 lutely none at all ; and that in other parts of the 

 world rocks of the very same formation are 

 crowded with the records of living forms, I think 

 it is impossible to place any reliance on the sup- 

 position, or to feel one's self justified in supposing 

 that these are the forms in which life first com- 

 menced. I have not time here to enter upon the 

 technical grounds upon which I am led to this 

 conclusion, that could hardly be done properly 

 in half a dozen lectures on that part alone : I 

 must content myself with saying that I do not 

 at all believe that these are the oldest forms 

 of life. 



I turn to the experimental side to see what 



