484 CONCLUSION. Chap. XIV. 



embraces all the members of the same class. I believe 

 that animals have descended from at most only four 

 or five progenitors, and plants from an equal or lesser 

 number. 



/'"Analogy would lead me one step further, namely, to 

 the belief that all animals and plants have descended 

 from some one prototype. But analogy may be a de- 

 ceitful guide. Nevertheless all living things have much 

 in common, in their chemical composition, their germinal 

 vesicles, their cellular structure, and their laws of growth 

 and reproduction. We see this even in so trifling a cir- 

 cumstance as that the same poison often similarly affects 

 plants and animals ; or that the poison secreted by the 

 gall-fly produces monstrous growths on the wild rose or 

 oak-tree. Therefore I should infer from analogy that 

 probably all the organic beings which have ever lived 

 on this earth have descended from some one primordial 

 form, into which life was first breathed. 



When the views entertained in this volume on the 

 origin of species, or when analogous views are generally 

 admitted, we can dimly foresee that there will be a con- 

 siderable revolution in natural history. Systematists 

 will be able to pursue their labours as at present ; but 

 they will not be incessantly haunted by the shadowy 

 doubt whether this or that form be in essence a 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 true 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 differences 

 be sufficiently important to deserve a specific name. 

 This latter point will become a far more essential con- 



