THE OLDEST AIR-BREATHERS 307 



hypothesis. It is the combination of various grades of reptilian 

 types in these ancient creatures. It has been well remarked 

 by Hugh Miller, and more fully by Agassiz, that this is charac- 

 teristic of the first appearance of new groups of animals. Now 

 selection, as it acts in the hands of the breeder, tends to 

 specialization ; and natural selection, if there is such a thing, is 

 supposed to tend in the same direction. But when some dis- 

 tinctly new form is to be introduced, an opposite tendency 

 seems to prevail, a sort of aggregation in one species of char- 

 acters afterward to be separated and manifested in distinct 

 groups of creatures. The introduction of such new types also 

 tends to degrade and deprive of their higher properties pre- 

 viously existing groups of lower rank. It is easy to perceive in 

 all this, law and order, in that higher sense in which these 

 terms express the will and plan of the Supreme Mind, but not 

 in that lower sense in which they represent the insensate 

 operation of blind natural forces. 



REFERENCES : " Air-breathers of the Coal Period." Montreal, 1886. 

 Papers on Reptiles, etc., in South Joggins Coal Field, Journal of 

 Geological Society of London, vols. ix. x. xi. xvi. Remains of Ani- 

 mals in Erect Trees in the Coal Formation of Nova Scotia, Trans. 

 Royal Society, 1881. "Acadian Gejplogy," fourth edition, 1891. Re- 

 vision of Land Snails of the Palaeozoic Era, Am. Journal of Science, 

 vol. xx., 1880. Supplementary Report to Royal Society of London, 

 Proceedings, 1892. Notice of additional Reptilian Remains, Geo- 

 logical Magazine of London, 1891. 



