200 CRITIQUES AND ADDRESSES. [ x. 



mation towards an estimate of the average rate of change 

 among the Sauropsida, it is almost appalling to reflect 

 how far back in Palaeozoic times we must go, before we 

 can hope to arrive at that common stock from which 

 the Crocodilia, Lacertilia, Ornithoscelida, and Plesio- 

 sauria, which had attained so great a development in 

 the Triassic epoch, must have been derived. 



The Amphibia and Pisces tell the same story. There 

 is not a single class of vertebrated animals which, when 

 it first appears, is represented by analogues of the lowest 

 known members of the same class. Therefore, if there is 

 any truth in the doctrine of evolution, every class must 

 be vastly older than the first record of its appearance 

 upon the surface of the globe. But if considerations of 

 this kind compel us to place the origin of vertebrated 

 animals at a period sufficiently distant from the Upper 

 Silurian, in which the first Elasmobranchs and Ganoids 

 occur, to allow of the evolution of such fishes as these 

 from a Vertebrate as simple as the Amphioxus, I can 

 only repeat that it is appalling to speculate upon the 

 extent to which that origin must have preceded the 

 epoch of the first recorded appearance of vertebrate life. 



Such is the further commentary which I have to offer 

 upon the statement of the chief results of palaeontology 

 which I formerly ventured to lay before you. 



But the growth of knowledge in the interval makes 

 me conscious of an omission of considerable moment in 

 that statement, inasmuch as it contains no reference to 

 the bearings of palaeontology upon the theory of the 

 distribution of life ; nor takes note of the remarkable 

 manner in which the facts of distribution, in present 

 and past times, accord with the doctrine of evolution, 

 especially in regard to land animals. 



That connection between palaeontology and geology 



