96 THE BEGINNINGS OF LIFE. 



aggregates (for compound molecules are such) are suc- 

 cessively generated ; as throughout Evolution in general. 

 More complex or heterogeneous aggregates are so made 

 to arise, one out of another; as throughout Evolution 

 in general. . . . And it is by the action of the suc- 

 cessively higher forms on one another, joined with the 

 action of environing conditions, that the highest forms 

 are reached ; as throughout Evolution in general x . 



If, however, we may suppose that by a process of 

 Evolution, under the influence of natural forces, any 

 such complex and unstable bodies as those to which 

 we have been referring could have come into being in 

 remote periods of the Earth's history, then scarcely any 

 conceivable limit could be placed upon the variations 

 which might still result under the continued play of 

 incident physical forces. In the first place, most of 

 these compounds whose molecules are very complex, 

 are found to be capable of existing -under many dif- 

 ferent isomeric modifications. Protein, for instance, 

 according to Prof. Frankland, is capable of existing 

 under probably at least a thousand isomeric forms ; and 

 this is the substance which, in one state or another, 

 enters so largely into the fabric of living things, as to 

 be, above all else, the organizable material. But even 

 this is not all; there are chemical possibilities more 

 favourable still for the origination and developmental 

 variation of living things. c There are facts,' Mr. 



1 Appendix to ' Principles of Biology ' (published separately), p. 482. 



