Evolution of Animal Life. 149 



artificial varieties of plants and animals, showing peculiar- 

 ities as marked as those of species. 



R. The intersterility of species and the interfertility of 

 varieties, together with the phenomena of aversion to the 

 ancestral form. 



V. Deductions from the Facts. 



We may for convenience recapitulate the foregoing facts 

 under brief titles, thus : 



A. Time ; B. Change of Environment ; C. Succession of 

 Forms ; D. Types ; E. Homologies ; F. Embryonic Stages ; 

 G. Geographical Distribution ; H. Direct Organic Modifi- 

 cations ; 7". Heredity ; K. Variation ; L. Multiplication ; M. 

 Population; N. Effective Life; 0. Competition; P. Pre- 

 mature Death; Q. Artificial Selection; R. Intersterility of 

 Species. 



And for further convenience, we may refer to these facts 

 by the letters which designate them, by which device we 

 shall be enabled to put in small space our summary state- 

 ment of the discussion. 



A to G inclusive are so much better explained on the 

 theory of some derivation of species by descent, than in any 

 other way, that Evolution, to this extent, may be said to 

 have been fairly established. In the present state of our 

 knowledge, we are obliged to say that the facts are as if 

 specific derivation had taken place, and we cannot believe 

 that either natural law or a rational Creator is mocking us 

 with delusive appearances. Nor do the advocates of inde- 

 pendent specific origins suggest any theory whatever to ex- 

 plain how these indications of relationship have been pro- 

 duced. 



G, it must be confessed, lends itself to either view, so far 

 as the distribution of species is the result of migration. 

 But in many respects, it is more in harmony with Evolution ; 

 and the one point which has been suggested as a difficulty, 

 namely, the absence of any shading-off or blending of spe- 

 cific peculiarities on the borders of the geographical habitat, 

 is founded in a misconception. " Missing links " are to be 

 sought in the past, not in the present ; at the junction of 

 branches, not in the air between their extremities. 



H is the " Lamarckian " factor, and, together with Z, was 

 principally relied upon in the theories of descent suggested 

 by Lamarck, the elder Darwin, Eobert Chambers (author of 



