44 
YAKIATION UNDEE NATUKE. 
Chap. II. 
CHAPTEE 11. 
Variation under Nature. 
Variability — Individual differences — Doubtful species — Wide 
ranging, much diffused, and common species vary most —Species 
of the larger genera in any country vary more than the species 
of the smaller genera — Many of the species of the larger genera 
resemble varieties in being very closely, but unequally, related 
to each other, and in having restricted ranges. 
Befoke applying the principles arrived at in the last 
chapter to organic beings in a state of nature, we must 
briefly discuss whether these latter are subject to any 
variation. To treat this subject at all properly, a long 
catalogue of dry facts should be given; but these I shall 
reserve for my future work. Nor shall I here discuss 
the various definitions which have been given of the 
term species. No one definition, has as yet satisfied all 
naturalists; yet every natm^alist knows vaguely what 
he means when he speaks of a species. Generally the 
term includes the unknown element of a distinct act of 
creation. The term ^^variety” is almost equally difficult 
to define; but here community of descent is almost 
universally implied, though it can rarely be proved. 
We have also what are called monstrosities; but they 
graduate into varieties. By a monstrosity I presume is 
meant some considerable deviation of structure in one 
part, either injurious to or not useful to the species, and 
not generally propagated. Some authors use the term 
variation” in a technical sense, as implying a modifica¬ 
tion directly due to the physical conditions of life; and 
variations ” in this sense are supposed not to be in¬ 
herited : but who can say that the dwarfed condition of 
shells in the brackish waters of the Baltic, or dwarfed 
