300 CONCLUSION. [Chap. XV, 



not it be accepted. No doubt it is possible, as Mr. G. 

 H. Lewes has urged, that at the first commencement of 

 life many difEerent forms were evolved; but if so, we 

 may conclude that only a very few have left modified 

 descendants. For, as I have recently remarked in regard 

 to the members of each great kingdom, such as the Ver- 

 tebrata, Articulata, &c., we have distinct evidence in 

 their embryological, homologous, and rudimentary struc- 

 tures, that within each kingdom all the members are 

 descended from a single progenitor. 



When the views advanced by me in this volume, and 

 by Mr. Wallace, or when analogous views on the origin 

 of species are generally admitted, we can dimly foresee 

 that there will be a considerable revolution in natural 

 history. Systematists will be able to pursue their la- 

 bours as at present; but they will not be incessantly 

 haunted by the shadowy doubt whether this or that form 

 be a true species. This, I feel sure and I speak after ex- 

 perience, will be no slight relief. The endless disputes 

 whether or not some fifty species of British brambles 

 are good species will cease. Systematists will have only 

 to decide (not that this will be easy) whether any form 

 be sufiiciently constant and distinct from other forms, 

 to be capable of definition; and if definable, whether 

 the differences be sufficiently important to deserve a 

 specific name. This latter point will become a far more 

 essential consideration than it is at present; for difEer- 

 ences, however slight, between any two forms, if not 

 blended by intermediate gradations, are looked at by 

 most naturalists as suQicient to raise both forms to the 

 rank of species. 



Hereafter we shall be compelled to acknowledge that 

 the only distinction between species and well-marked 



