LIFE ON THE EARTH. 83 



Palaeozoic Period ... Brachwpodu, Gasteropoda, Zoophyta, 

 Dimyaria, Cephalopoda, Echinodermata, 

 Crustacea, Monomyaria. 



Taken in the order of their total numerical su- 

 periority, the classes range thus : 



Caenozoic. Mesozoic. Palaeozoic. Total. 



Gasteropoda 662+ 389 401 1452 



Dimyaria 394 499+ 342 1235 



Brachiopoda 8 165 632+ 805 



Cephalopoda 12 396+ 336 744 



Monomyaria 63 308+ 196 567 



Echinodermata ... 41 245+ 225 511 



Zoophyta 27 103 379+ 509 



Crustacea 15 65 218+ 298 



The sign + is placed to the maximum number 

 in each class, shewing that the maximum is attained 

 in the 



Caenozoic Period, by Gasteropoda. 



Mesozoic Period, by Dimyaria, Cephalopoda, Monomyaria, 



Echinodermata. 

 Palaeozoic Period, by Brachiopoda, Zoophyta, Crustacea. 



These results afford but slight encouragement to 

 the speculation of the inferiority of the earlier and 

 superiority of the later systems, and of continual 

 progress upward in the organization of animals. In 

 proportion to the elapsed time the changes make 

 progress, but these changes are not always in the 

 sense of uninterrupted advance from inferior to 

 superior forms. 



G2 



