IN MODERN SCIENCE. 



IE I 



into the Cambrian or Lower Silurian ocean, 

 we should have brought up representatives of 

 all the leading types of invertebrate life that 

 exist in the modern seas^ — different, it is true, 

 in details of structure from those now existing, 

 but constructed on the same principles and fill- 

 ing the same places in nature. 



If we inquire as to the history of this swarm- 

 ing marine life of the early Palaeozoic, we find 

 that its several species, after enduring for a 

 longer or a shorter time, one by one became 

 extinct and were replaced by others belonging 

 to the same groups. Thus there is in each 

 great group a succession of new forms, distinct 

 as species, but not perceptibly elevated in the 

 scale of being. In many cases, indeed, the re- 

 verse seems to be the case; for it is not un- 

 usual to find the successive dynasties of life in 

 any one family manifesting degradation rather 

 than elevation. New, and sometimes higher, 

 forms, it is true, appear in the progress of time, 

 but it is impossible, except by violent supposi- 

 tions, to connect them genetically with any pre^ 

 decessors. The succession throughout the Pa- 

 laeozoic presents the appearance rather of the 

 unchanged persistence of each group under a 

 succession of specific forms, and the introduc- 



