8G M. Bronn on the Laws of Evolution of the Organic World 



of creation in the series of geological ages lias taken place with 

 a perfect consequentially and in a perfectly independent manner. 

 Systematic and progressive development, and the law which 

 governs it, are facts which can no longer be misconceived. Never- 

 theless we must not represent this progressive development as 

 consisting in the primitive appearance of the Phytozoa alone, 

 which would be followed by the Actinozoa, then by the Malacozoa, 

 then by the Entomozoa, and finally by the Spondylozoa, each 

 class and each order being followed by the appearance of a class 

 or order occupying a higher place in the scale of organization. 

 In reality, the subkingdoms, for which the external conditions 

 of existence at the most ancient period were sufficient, made 

 their appearance simultaneously, or nearly so. These subking- 

 doms were represented by the classes and orders lowest in 

 organization — by pelagic, swimming forms, respiring air by 

 means of branchiae. When, subsequently, the superior sub- 

 kingdoms were rapidly created one after the other, the classes 

 and orders which had first appeared were represented by types 

 gradually ascending. This is what we observe in many cases, 

 and in all the subkingdoms without exception, when we pass 

 them in review class by class and order by order, so as to prove 

 the period of their appearance and that of their culmination 

 (appearance of the higher plants, the bony fishes, the mammalia). 



13. This plan of succession is nowhere more evident than in 

 the vegetable kingdom, in which we see several subkingdoms 

 appear at first and simultaneously, followed by the successive 

 appearance of the superior groups most nearly allied to them in 

 organization, and which only attained their culmination subse- 

 quently. The perfectly natural consequence of this, was the com- 

 paratively far later appearance of the most highly organized groups 

 of plants — groups which surpass all the others in the number of 

 their genera and species ; and yet, at least as far as we can now 

 judge, the external conditions of existence would have permitted 

 their appearance from the very first. It is not possible for us, now- 

 a-days, to ascertain any cause to which may have been due the 

 retardation of the appearance of the angiospermous Dicotyledons 

 until the cretaceous epoch*, except the law of progressive develop- 

 ment (at least unless we choose to assume that the emission of 

 carbonic acid in the ancient epochs may have opposed their 

 production). 



14. The late appearance of the angiospermous Dicotyledons is 

 undoubtedly, of all causes, that which had the most importance 

 in retarding the appearance of most of the terrestrial animals, 

 such as the insects, birds, and mammalia. In all cases, the 



* We must recollect that at least one angiosperni has heeu quoted from 

 the Coal-measures. See LyelPs 'Manual,' 1855, p. 374. — Ed. Annals. 



