sect, iv.] INTRODUCTION. 17 



To sum up : 



The first question which the Study of Variation may be ex- 

 pected to answer, relates to the origin of that Discontinuity of 

 which Species is the objective expression. Such Discontinuity 

 is not in the environment ; may it not, then, be in the living 

 thing itself? 



The Study of Variation thus offers a means whereby we may 

 hope to see the processes of Evolution. We know much of what 

 these processes may be : the deductive method has been tried, 

 with what success we know. It is time now to try if these things 

 cannot be seen as they are, and this is what Variation may shew 

 us. In Variation we look to see Evolution rolling out before our 

 eyes. In this we may fail wholly and must fail largely, but it 

 is still the best chance left. 



SECTION IV. 

 Symmetry and M eristic Repetition. 



Having thus indicated some of the objects which we may 

 hope to reach by the Study of Variation, we have next to consider 

 the way in which to set about this study. 



The Study of Variation is essentially a study of differences 

 between organisms, so for each observation of Variation at least 

 two substantive organisms are required for comparison. It is 

 proposed to confine the present treatment of the subject to a 

 consideration of the integral steps by which Variation may pro- 

 ceed ; hence it is desirable that the two organisms compared 

 should be parent and offspring, and if, as is often the case, the 

 actual parent is unknown, it is at least necessary that the normal 

 form of the species should be known and that there must be 

 reasonable evidence that the varying offspring is actually de- 

 scended from such a normal. For this reason, evidence from a com- 

 parison of Local Races, and other established Varieties, though a 

 very valuable part of the Study, will for the most part not be here 

 introduced. For the belief that such races are descended from the 

 putative normal scarcely ever rests on proof, and still more rarely 

 is there evidence of the number of generations in which the 

 change has been effected. 



For our purpose we require actual cases of Variations occurring 

 as far as possible in offspring of known parentage ; and if, failing 

 this, we make use of cases occurring in the midst of normal indi- 

 viduals of known structure, it must in such cases be always 

 remembered that we cannot properly assume that the varying form 

 is the offspring of such individuals, though special reasons may 

 make this likely in special cases. 



Since the structure of the offspring is perhaps in no case 

 b. 2 



