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faunas of the more ancient formations are far less imperfect than 

 has been often supposed. The vertebrate type is already represented 

 in them by the fishes, and the different classes of the invertebrata 

 are by no means reduced to their less complex forms of organization, 

 since, among the moUusca for example, we find numerous examples 

 of gasteropoda and cephalopoda, the most perfect orders of the 

 class. It cannot be said therefore with regard to the invertebrata, 

 that the faunas of the more ancient formations exhibited organiza- 

 tion inferior to that presented in newer deposits ; and the most that 

 can be asserted is, that among the vertebrata the most highly or- 

 ganized animals of the oldest period seem to have been fishes. If 

 then we would deduce the true character of most ancient faunas, we 

 shall find that they bear comparison with the groups of existing ani- 

 mals, excluding reptiles, birds and mammalia, and that all the 

 types, including those of fishes, were then represented by animals as 

 perfect as those of the present day. 



" The intermediate faunas, such as that of the Oolitic period, dif- 

 fered from those of the earlier and later periods by analogous cha- 

 racters. The fishes, the mollusca, the articulata and the radiata, 

 compared with the preceding and succeeding forms, exhibit similar 

 organization neither more nor less perfect. But these intermediate 

 faunas differed from the earlier ones yet further, since the vertebrata 

 in them included reptiles and didelphine mammals, while they dif- 

 fered from the more modern ones by the absence of the monodel- 

 phous mammals. 



" We shall find then that neither the radiata, nor the articulata, nor 

 the mollusca, nor the fishes, were imperfectly developed in ancient 

 times, and that ever since their first appearance the species belong- 

 ing to these classes of animals have possessed the same degree of 

 perfection as those that live now. It is therefore a mistake to sup- 

 pose that the early faunas generally were composed of animals less 

 perfect than the recent ones, although indeed we find that the high- 

 est point to which organization reached has risen during successive 

 geological periods; so that while fishes at first formed the superior 

 limit of organization, they were afterwards surpassed by the reptiles, 

 and these also, after an interval, by the mammals. 



" To such greatly narrowed limits therefore, the law we are dis- 

 cussing must now be reduced. It is not true when applied to or- 

 ganization generally, but it expresses a fact when so limited as to 

 mean only *the appearance of the higher forms of organization'; 

 and thus limited, it will even, according to the present state of our 

 knowledge, hardly serve to establish the notion of a marked supe- 

 riority in the existing faunas. With reference to this point however 

 I will conclude with two observations. 



" The first is, that we ought not to be too hasty in assuming the 

 absence of certain more perfect types in the older faunas merely be- 

 cause we have not yet discovered any remains of them. We hardly 

 know anything of these faunas, except with regard to some of the 

 inhabitants of the sea, and it is well known that in the present con- 

 dition of the globe, those animals living on land exhibit the higher 



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