io8 



ORGANIC EVOLUTION 



are living to-day in the lakes of Slavonia. These lakes 

 have been gradually filled up by the silt brought into them 

 by their tributary streams. Careful study of the deposits 



FIG. 26. Successive forms of Paludina from the tertiary deposits of Slavonia. From 

 Romanes" Darwin and after Darwin, by the courtesy of The Open Court Publishing Company. 



thus formed has brought to light a remarkably complete 

 series of fossil Paludina shells. The uppermost of these, 

 those nearest the surface and last deposited, are identical 

 with the forms now living in the same region. As we go 



