XXVIII 



ON CERTAIN ZOOLOGICAL ARGUMENTS COMMONLY 

 ADDUCED IN FAVOUR OF THE HYPOTHESIS OF 

 THE PROGRESSIVE DEVELOP:\IENT OF ANIMAL 

 LIFE IN TIME 



Friday, April 20, 1S55 

 Roy. Inst. Proc, vol. ii., 1854-58, //. 82-85 



When the fact that fossilized animal forms are no lusns naturcE, 

 but are truly the remains of ancient living worlds, was once fully 

 admitted, it became a highly interesting problem to determine 

 what relation these ancient forms of life bore to those now in 

 existence. 



The general result of inquiries made in this direction is, that the 

 further we go back in time, the more different are the forms of life 

 from those which now inhabit the globe, though this rule is by no 

 means without exceptions. Admitting the difference, however, the 

 next question is, what is its amount ? Now it appears, that while the 

 Palaeozoic species are probably always distinct from the modern, and 

 the genera are very commonly so, the orders are but rarely different, 

 and the great classes and sub-kingdoms never. In all past time we 

 find no animal about whose proper sub-kingdom, whether that of the 

 Protozoa, Radiata, Annulosa, Mollusca, and Vertebrata, there can be 

 the slightest doubt ; and these great divisions are those which we 

 have represented at the present day. 



In the same way, if we consider the Classes, eg. Mamvialia, Aves, 

 Insecta, Cephalopoda, Actinosoa, Sac, we find absolutely no remains 

 which lead us to establish a class type distinct from those now 

 existing, and it is only when we descend to groups having the rank 

 of Orders that we meet with types which no longer possess any living 

 representatives. It is curious to remark again, that, notwithstanding 



