PROGRESS IN THE STUDY OF VARIATION. 557 



examination of one species or one character to the problems 

 presented by other species or other characters. The pro- 

 perties of species are in brief specific, as the properties of 

 chemical substances are ; and as the properties of each 

 chemical substance have to be separately determined, so 

 must the specific properties of each species be the subject 

 of separate and special study. In what may be called the 

 Chemistry of Species we are far indeed from the era of 

 o-eneralisation. 



Discontinuity in variation is in great numbers of cases 

 an observed fact, while the supposition that when organisms 

 are freely breeding together in the state of nature all the 

 varieties they display in size, colour, structure, and so forth, 

 are capable of freely blending, and that the offspring of dis- 

 similar parents tend always to regress to one mean form 

 is not borne out by the facts. Whether continuity or dis- 

 continuity is found depends on the species studied and the 

 character selected for investigation. There is continuous 

 variation, but there is discontinuous variation also. To 

 discover by statistical investigation the degree of continuity 

 or discontinuity which in each species is manifested by the 

 variation of each character is the first business of the student 

 of evolution. 



Those who do not admit the probability that discon- 

 tinuous variation may have a preponderating influence in 

 the establishment of new species will remember that this is 

 confessedly a matter for individual judgment, and whatever 

 views may be entertained on this matter the fact that dis- 

 continuity is frequent in variation remains indisputable. 

 Indeed, if it is admitted that the problem of evolution is to 

 be attacked by the study of variation no assumption need 

 be made to justify the prerogative claims of cases in which 

 there is an appearance of discontinuity ; for discontinuous 

 varieties have, prima facie, already something of specific 

 distinctness, and whether they are or are not those nascent 

 species we are all seeking, they at least look more like them 

 than other varieties do. 



We are in a preliminary stage, and apart even from any 

 question of continuity or discontinuity it is surely well that 



