THE BRITISH FOSSIL BRACHIOPODA. 



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Quaternary 



Tertiary 



Secondary 



Permian and Carboniferous . 



Devonian 



Silurian 



Cambrian 



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truth we must add that the actual state of our scientific knowledge will scarcely admit of our going 

 further. The primordial fossils have not hitherto furnished material proof of passages from one class of 

 animals into another. This statement will not surprise naturalists ; for the larger number of them 

 scarcely believe in a linear series, commencing at the Monad, and continuing turn by turn under 

 the form of Polypi, of Echinoderm, of Mollusc, of Annelid, of Articulate, of Fish, of Reptile, of 

 Bird, of Mammal, and finishing with Man. For example, although the Mammalia are the most 

 perfect among the Vertebrates, embryology does not show that they have passed through the condition 

 of Fish, Saurians, and Bird. It is very likely that in geological times there has not been simply a single 

 chain, but many concatenations. The animals of different classes seem to have formed at a very early 

 period distinct branches, of which the development has gone on in an independent manner. While 

 supposing that the palseontological history of the world presents to us a series of evolutions, we must 

 admit that there has existed great inequalities in the development of animals. These inequalities 

 do not confirm the idea of a struggle for existence in which victory remained with the strongest or 

 the most favoured ; it is sometimes the beings the most favoured and the most perfect in their 

 class that have become extinct the soonest : Paradoxides of the Cambrian, Slimonia of the Silurian, 

 Pterichthys of the Devonian, Pentremites of the Carboniferous, Euchirosanrus of the Permian, have 

 marked the highest point of divergence to which their type was to obtain ; they could not therefore 

 produce new forms ; and as the peculiar quality of the larger number of creatures is to change or to 

 die, they became extinct. At the side of these creatures which have been as passage kings, there have 

 been others of which the personality was less decided, creatures of a more mixed nature, representing 

 in the animal world the just medium. Among these we find the types that have had the greatest 

 persistence. Thus in our days certain cosmopolitan forms are found in every country ; and these forms 

 one might term ' panchronique,' for they are of every epoch. They have formed as it were a permanent 

 reservoir, from which have issued at each instant of geological time creatures destined to assume a more 

 or less important part. If these various creatures had changed equally rapidly, those that have been 

 transmitted to us from past ages would all now be animals of a high order ; there would thus be more animals 

 that eat than beasts to be eaten ; and the harmony of the organic world would have long since been broken. 



