128 THE GENESIS OF SPECIES. [CHAP 



tion : one individual lies near one portion of the surface ; 

 another individual, of the same species, near another part 

 of the surface ; the average animal at the centre. Any in- 

 dividual may produce descendants varying in any direction, 

 but is more likely to produce descendants varying toward 

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

 will be greater in amount than the variations toward the 

 surface." This might be taken as the representation of the 

 normal condition of species (i. e., during the periods of re- 

 pose of the several facets of the spheroids), on that view 

 which, as before said, may yet be 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 

 correspondence with surrounding conditions ; but 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, 3 " Crystalline formation is also de- 

 pendent in a very remarkable way on the medium in which 

 it takes place." " Beudant has found that common salt, 

 crystallizing from pure water, forms cubes ; but if the water 

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

 truncated. And the Rev. E. Craig has found that carbon- 

 ate of copper, crystallizing from a solution containing sul- 

 phuric acid, forms hexagonal tubular prisms ; but if a little 

 ammonia is added, the form changes to that of a long, rec- 

 tangular prism, with secondary planes in the angles. If a 

 little more ammonia is added, several varieties of rhombic 

 octahedra appear ; if a little nitric acid is added, the rec- 

 tangular prism appears again. The changes take place not 

 by the addition of new crystals, but by changing the growth 



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



