64 
however great, remains constantly small in comparison to those that 
are possible, consequently do not give by their magnitude any certain 
measure of periods of time. 
‘The correctness of the above expositions is not founded on indi- 
vidual opinion formed from hasty imspections of petty objects; but 
the microscopic objects on which the opinions are based (though 
fading from our notice as individuals, yet by their number forming 
mountains and countries) are accessible to any comparison in distinct 
preparations, made according to the methods already described ; and 
almost all the forms here mentioned, especially all the more import- 
ant ones, have been carefully preserved by me, and laid before the 
Academy. 
“Thus then there is a chain, which though in the individual it be 
microscopic, yet in the mass a mighty one, connecting the organic life 
of distant ages of the earth, and proving that it is not always the 
smaller or most deeply lying which is the base and the type of those 
which are larger and nearer the surface on our earth ; and moreover, 
that the dawn of the organic nature coexistent with us, reaches further 
back into the history of the earth than had hitherto appeared.” 
These discoveries, by so accurate an observer as Professor Ehren- 
berg, have to a certain degree modified the views as to the period of 
introduction of existing animated species. No recent beings were con- 
sidered before this statement to be specifically the same as the fossils 
observed in the secondary period; yet it has been shown that fifty- 
seven species are clearly made out to be identical. I am willing to 
admit that small bodies are difficult of examination, and require a 
great nicety of microscopical observation ; but it must also be allowed, 
that, in the supposed changes which the world has undergone, no ma- 
terial alteration has taken place im the chemical composition of sea- 
water; and from the myriads of Infusoria that must have been in 
