SPECIES BY mFINITESIMAL VARIATIONS. 15 



completely disproves the theory of origin of species by natural 

 selection of infinitesimal variations, and gives strong evidence 

 in favour of origin by mutation. The evidence cannot, I 

 think, be disputed for the case of the endemics of the summit 

 of Ritigala. It is equally good for the endemics of Ceylon, 

 Mauritius, or New Zealand, and this being so, analogy of the 

 characters that divide species all over the world (for, of course, 

 the systematists have worked at specific distinction regardless 

 of any theory of the origin of species) shows that this must be 

 a perfectly general rule, and consequently that the theory of 

 infinitesimal variations as the foundation of the origin of 

 species must be given up. 



The theory of mutation, on the other hand, will explain all 

 the cases that have been brought forward, though why muta- 

 tion should proceed in this apparently casual manner must 

 for the present remain a puzzle. It is possible, if not probable, 

 that a group of allied species represents so many more or less 

 stable position.^ of equilibrium in cell-division, and it is 

 at least entirely doubtful if any given species is specially 

 adapted for the circumstances in which it is found. This 

 adaptation , though of course certain for whole groups of plants , 

 such as water plants or parasites, must be proved for each 

 instance 



We shall follow this paper with others dealing in detail with 

 the many interesting points here raised. 



