296 GEOLOGICAL BIOLOGY. 



laws are always found together in the same organism. Each 

 individual organism is the source and record of those facts 

 which we separately interpret as evidence of cell-growth, in- 

 dividual growth, the differentiation of organs, and the phylo- 

 genetic evolution. 



Thus there are series of organic forms succeeding each 

 other in some regular order, known or unknown, which are 

 bound together by organic, and in this case called particularly 

 genetic relationship. The changes in form observed upon 

 comparing the individuals at different points in the line of 

 succession are accounted for by some law of evolution, and 

 the origin of the different members of the series is said to be 

 by generational descent, the later arising from the earlier. 

 On account of the mutability of form in the process, species 

 presenting different form, different function, and incapable of 

 organic fertility are supposed to have arisen originally from 

 a common parentage. 



Mutability the Fundamental Law of Organisms ; the Acquire- 

 ment of Permanency Secondary. — This analysis brings us face 

 to face with one of the chief inconsistencies in the prevalent 

 conception of the nature of organisms. While the doctrine 

 of mutability of species has generally taken the place of im- 

 mutability, the proposition that like produces like in organic 

 generation is still generally, and I suppose almost universally, 

 accepted. It therefore becomes necessary to suppose that 

 variation is exceptional, and that some reason for the accumu- 

 lation of variation is necessary to account for the great diver- 

 gencies seen in different species. Darwin's theory of natural 

 selection is chiefly concerned in accounting for the accumula- 

 tion, increase, and perpetuation of divergencies arising by 

 natural variation. 



If we extend the principle of mutability, and instead of 

 regarding it as an accidental circumstance in the life-history 

 of organisms, recognize it as the distinctive and fundamental 

 characteristic of living beings, we escape this inconsistency. 



In the physical and chemical world like causes do pro- 

 duce like effects; but in the organic world like produces like 

 " with an increment," as Professor J. D. Dana put it. Muta- 

 bility and variation are evidences of this increment. The 



