ever 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. Thus, Dr. S.P.
Woodward states that many present a most perplexing amount of variation,
resulting (as he supposes) from supply of food, variety of depth and of
saltness of the water; but we know that many variations are quite
independent of such causes, and we will now consider a few cases among
the land-mollusca in which they have been more carefully studied.

In the small forest region of Oahu, one of the Sandwich Islands, there
have been found about 175 species of land-shells represented by 700 or
800 varieties; and we are told by the Rev. J.T. Gulick, who studi