378 THE CAUSES OF THE XI 
which is also a crustacean. So that you have all — 
the Fawna 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 im 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 
