e more and more out of water, and to breathe the
air. For these species, from belonging to distinct families, would have
differed to a certain extent, and in accordance with the principle that
the nature of each variation depends on two factors, viz., the nature of
the organism and that of the surrounding conditions, their variability
assuredly would not have been exactly the same. Consequently natural
selection would have had different materials or variations to work on,
in order to arrive at the same functional result; and the structures
thus acquired would almost necessarily have differed. On the hypothesis
of separate acts of creation the whole case remains unintelligible. This
line of argument seems to have had great weight in leading Fritz Muller
to accept the views maintained by me in this volume.

Another distinguished zoologist, the late Professor Claparede, has
argued in the same manner, and has arrived at the same result. He
shows that there are parasitic mites (Acaridae), belonging to distinct
sub-families and families, which are furnished with hair-claspers. These
organs must have been independently developed, as they could not have
been inherited from a common progenitor; and in the several groups they
are formed by the modification of the fore legs, of the hind legs, of
the maxillae or lips, and of appendages on the under side of the hind
part of the body.

In the foregoing cases, we see the same end gained and the same function
performed, in beings not at all or only remotely allied, by organs in
appearance, though not in development, closely similar. On the other
hand, it is a common rule throughout nature that the same end should
be gained, even sometimes in the case of closely related beings, by the
most diversified means. How differently constructed is the feathered
wing of a bird and the membrane-covered wing of a bat; and still more so
the four wings of a butterfly, the two wings of a fly, and the two wings
with the elytra of a beetle. Bivalve shells are made to open and shut,
but on what a number of patterns is the hinge constructed, from the long
row of neatly interlocking teeth in a Nucula to the simple ligament of
a Mussel! Seeds are disseminated by their minuteness, by their capsule
being converted into a light balloon-like envelope, by being embedded
in pulp or flesh, formed of the most diverse parts, and rendered
nutritious, as well as conspicuously coloured, so as to attract and
be devoure