CflAP. XIV. CONCLUSION. 433 



the members of each great class, such as the Vertebrata, Artio- 

 ulataj etc., Ave have distinct evidence in their embryological, 

 homologous, and rudimentary structures, that within each class 

 all are descended from a single progenitor. 



When the views advanced by me in this volume, and by 

 Mr. Wallace in the Linncan Journal, or when analogous views 

 on the origin of species are generally admitted, Ave can dimly 

 foresee that there will be a considerable revolution in natural 

 liistory. Systematists will be able to pursue their labors as at 

 present ; but they Avill not be incessantly haunted by the shad- 

 owy doubt whether this or that form be a true species. This 

 I feel sure, and I speak after experience, will be no slight re- 

 lief. 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 definable, whether the dif- 

 ferences be sufficiently important to deserve a specific name. 

 Tliis latter point Avill 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 Ave shall be compelled to 

 acknoAvledgc that the only distinction Ijctween species and 

 Avell-maiked varieties is, that the latter arc knoAvn, or believed, 

 to be connected at the ]iresent day by intermediates gradations, 

 whereas species Avere formerly thus connected. Hence, Avith- 

 out rejecting the consideration of the present existence of in- 

 Icnnediate gradations between any two forms, Ave shall be led 

 to Avelgh more carefully and to A'alue higher the actual amount 

 of dillcrence between them. It is quite jiossible that forais noAV 

 generally acknowledged to be merely varieties may hereafter 

 l)o thought Avorthy of specific names ; and in this case scien- 

 tific and common language Avill come into accordance. In 

 short, Ave shall liaA'C to treat species in the same manner as 

 those naturalists treat genera, Avho admit that genera are 

 merely artificial combinations made for conA'cnience. Tliis 

 may not be a cheering prospect; but avc shall at least be freed 

 from the A'ain search for the undiscovered and undiscoverable 

 essence of the term sj)ecies. 



The other and more general departments of natural history 

 Avill rise greatly in interest. The terms used l>y naturalists of 

 allinitv, relationship, community of type, paternitv, morpholo- 

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