Wild animals and plants, it is said, are usually stable, and when variations occur these are alleged to be small in amount and to affect superficial characters only; or if larger and more important, to occur so rarely as not to afford any aid in the supposed formation of new species.
This objection, as will be shown, is utterly unfounded; but as it is one which goes to the very root of the problem, it is necessary to enter at some length into the various proofs of variation in a state of nature.
This is the more necessary because the materials collected by Mr.Darwin bearing on this question have never been published, and comparatively few of them have been cited in _The Origin of Species_; while a considerable body of facts has been made known since the publication of the last edition of that work.
_Variability of the Lower Animals_.
Among the lowest and most ancient marine organisms are the Foraminifera, little masses of living jelly, apparently structureless, but which secrete beautiful shelly coverings, often perfectly symmetrical, as varied in form as those of the mollusca and far more complicated.

These have been studied with great care by many eminent naturalists, and the late Dr.W.B.Carpenter in his great work--the _Introduction to the Study of the Foraminifera_--thus refers to their variability: "There is not a single species of plant or animal of which the range of variation has been studied by the collocation and comparison of so large a number of specimens as have passed under the review of Messrs.

Williamson, Parker, Rupert Jones, and myself in our studies of the types of this group;" and he states as the result of this extensive comparison of specimens: "The range of variation is so great among the Foraminifera as to include not merely those differential characters which have been usually accounted _specific_, but also those upon which the greater part of the _genera_, of this group have been founded, and even in some instances those of its _orders_."[16] Coming now to a higher group--the Sea-Anemones--Mr.P.H.

Gosse and other writers on these creatures often refer to variations in size, in the thickness and length of the tentacles, the form of the disc and of the mouth, and the character of surface of the column, while the colour varies enormously in a great number of the species.

Similar variations occur in all the various groups of marine invertebrata, and in the great sub-kingdom of the mollusca they are especially numerous.