254 THE CHAIN OF LIFE. 



As to tlic first of these questions, it is certain that, up to 

 this time, the origination of the living being from the n.jn- 

 living is an inscrutable mystery. No one has witnessed this 

 change, or has been able to effect it experimentally. Nor have 

 we any direct evidence of the origination of one spec:ific type 

 from another. Such rensonings as assume the possilMlity of 

 tlicsc things, or on analogical grounds assert their probability, 

 belong rather to the domain of philosophicai speculation than 

 to science. As to the laws of the succession of life, however, 

 it is possible to learn something from the sccjuence of facts 

 as already ascertained ; and though much rem. ins to be dis- 

 covered, there are a few leading statements on this subject 

 which can already be made with safety. 



Unity and uniformity, within the limits imposed by progress 

 and increasing complexity, can be affirmed of the whole 

 process. From the dawn of life to the present time the 

 great laws of i)hysical nature which oi)erate on animals and 

 T)larits have been uniform. These stable laws have regulated 

 the action of the outer world on organisms. The plans of 

 structure of these organisms laid down at the iirst have been 

 followeil throughout. Thus the succession of life presents 

 nothing fortuitous or arljitrary, but a continuous plan carried 

 out uniformly in time and space, with certain materials of fixed 

 properties, and with certain structures predetermined from the 

 first. There is, for example, a great sameness of ])lan throughout 

 the whole history of the marine invertebrate life of the Palaeo- 

 zoic. If we turn over the pages of an illustrated text-book of 

 geology, or examine the cases or drawers of a collection of 

 fossils, we shall find extending through every succeeding forma- 

 tion, representative forms of Crustaceans, Mollusks, and Corals, 

 in suc'i :■ manner as to indicate that in each successive i)erio(l 

 tliere has been a reproduction of the same type with modifica- 

 tions; and if the series is not continuous, this ai)pears to be 

 due to lack of specimens, or to abru}>t physical changes ; since 

 sometimes, where two formations pass into each other, we find 



