A view as to the stability of species, in the intervals of change, has been well expressed in an able article, before quoted from, as follows:[104]--"A given animal or plant appears to be contained, as it were, within a {114} sphere of variation: 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 individual may produce descendants varying in any direction, 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 representation of the normal condition of species (_i.e._ during the periods of repose 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 crystallized 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,[105] "Crystalline formation is also dependent 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 carbonate of copper, crystallizing from a solution containing sulphuric acid, forms hexagonal tubular prisms; but if a little ammonia is added, the form changes to that of a long rectangular 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 rectangular prism appears again. The changes take place not by the addition of new crystals, but by changing the growth of the original ones." These, however, may be said{115} to be the same species, after all; but recent researches by Dr. H. Charlton-Bastian seem to show that modifications in the conditions may result in the evolution of forms so diverse as to constitute different organic species.