f antelopes until the present day. But it is
in the deer tribe that we meet with even better evidence touching the
progressive evolution of horns; because here not only size, but shape,
is concerned. For deer's horns, or antlers, are arborescent; and hence
in their case we have an opportunity of reading the history, not only of
a progressive growth in size, but also of an increasing development of
form. Among the older members of the tribe, in the lower Miocene, there
are no horns at all. In the mid-Miocene we meet with two-pronged horns
(_Cervus dicrocerus_, Figs. 61, 62, 1/5 nat. size). Next, in the upper
Miocene (_C. matheronis_, Fig. 63, 1/8 nat. size), and extending into
the Pliocene (_C. pardinensis_, Fig. 64, 1/18 nat. size), we meet with
three-pronged horns. Then, in the Pliocene we find also four-pronged
horns (_C. issiodorensis_, Fig. 65, 1/16 nat. size), leading us to
five-pronged (_C. tetraceros_). Lastly, in the Forest-bed of Norfolk we
meet with arborescent horns (_C. Sedgwickii_, Fig. 66, 1/35 nat. size).
The life-history of existing stags furnishes a parallel development
(Fig. 67), beginning with a single horn (which has not yet been found
palaeontologically), going on to two prongs, three prongs, four prongs,
and afterwards branching.

[Illustration: FIG. 60.--Skull of _Oreodon Culbertsoni_. (After
Leidy.)]

[Illustration: FIGS. 61-66. The series is reduced from Gaudry's
illustrations, after Farge, Croizet, Jobert and Boyd Dawkins.]

[Illustration: FIG. 67.--Successive stages in the development of an
existing Deer's Antlers. (After Gaudry, but a better illustration
has already been given on p. 100.)]

* * * * *

Coming now to bones, we have a singularly complete record of transition
from one type or pattern of structure to another in the phylogenetic
history of tails. This has been so clearly and so tersely conveyed by
Prof. Le Conte, that I cannot do better than quote his statement.

It has long been noticed that there are among fishes two styles of
tail-fins. These are the even-lobed, or homocercal (Fig. 68), and
the uneven-lobed, or heterocercal (Fig. 69). The one is
characteristic of ordinary fishes (teleosts), the other of sharks
and some other orders. In structure the difference is even more
fundamental than in form. In the former style the backbone stops
abruptly in a series of short, enlarged join