conclusion: 501 



brata, Articulata, etc., we have distinct evidence in their 

 embryological, homologous, and rudimentary structures, 

 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 labors as at pres- 

 ent; 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 experience, 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 sufficiently constant and distinct 

 from other forms, to be capable of definition; and if defina- 

 ble, 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 

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

 blended by intermediate gradations, are looked at by most 

 naturalists as sufficient 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 varie- 

 ties is, that the latter are known, or believed to be con- 

 nected at the present day by intermediate gradations, 

 whereas species were formerly thus connected. Hence, 

 without rejecting the consideration of the present existence 

 of intermediate gradations between any two forms, we 

 shall be led to weigh more carefully and to value higher 

 the actual amount of difference between them. It is quite 

 possible that forms now generally acknowledged to be 

 merely varieties may hereafter be thought worthy ' of 

 specific names; and in this case scientific and common lan- 

 guage will come into accordance. In short, we shall have 

 to treat species in the same manner as those naturalists 

 treat genera, who admit that genera are merely artificial 

 combinations made for convenience. This may not be a 

 cheering prospect; but we shall at least be freed from the 

 vain search for the undiscovered and undiscoverable 

 essence of the term species. 



