128 THE GENESIS OF SPECIES. [CHAP. 



quoted from, as follows: 1 "A given animal or plant 

 appears to be contained, as it were, within a sphere of 

 variation : one individual lies near one portion of the sur- 

 face ; another individual, of the same species, near another 

 part of the surface ; the average animal at the centre. Any 

 individual may produce descendants varying in any direc- 

 tion, but is more likely to produce descendants varying 

 towards the centre of the sphere, and the variations in that 

 direction will be greater in amount than the variations 

 towards the surface." This might be taken as the repre- 

 sentation of the normal condition of species (i.e. during 

 the periods of repose of the spheroids upon their several 

 facets) assuming as true that specific stability which has 

 been before defended. 



Judging the organic world from the inorganic, we might 

 expect a priori that each species of the former, like crys- 

 tallized species, would have an approximate limit of form 

 and even of size, and at the same time that the organic, like 

 the inorganic forms, would present modifications in corre- 

 spondence with surrounding conditions ; yet that these 

 modifications would be, not minute and insignificant, but 

 definite and appreciable, equivalent to the shifting of the 

 spheroid on to another facet for support. 



Mr. Murphy says, 2 " Crystalline formation is also depen- 

 dent in a very remarkable way on the medium in which it 

 takes place." " Beudant has found that common salt crys- 

 tallizing from pure water forms cubes, but if the water 

 contains a little boracic acid, the angles of the cubes are 

 truncated. And the Eev. E. Craig has found that carbonate 

 of copper, crystallizing from a solution containing sulphuric 



1 North British Review, New Series, vol. vii., March 1867, p. 282. 



2 "Habit and Intelligence," vol. i. p. 75. 



