| | |
C | Jurassic,........|.........|...........|......
O | | | |
N | Triassic,........|.........|...........|......
D | | | |
A | Permian,.........|.........|...........|......
R | | | |
Y | Carboniferous,...|.........|.........Insects..
| |
P | | |
R | Devonian,........|.........|..................
I | | |
M | Silurian,.....Worms. Crustacea...............
A |
R | Azoic.
Y |

VERTEBRATES.
Fishes. Reptiles. Birds. Mammalia.
T | Present,.........|.........|.........|........|.......
E | | | | |
R | Pliocene,........|.........|.........|........|.......
T | | | | |
I | Miocene,.........|.........|.........|........|.......
A | | | | |
R | Eocene,..........|.........|.........|..True Mammalia.
Y | | | | |
| | | |
S | Cretaceous,......|.........|.........|........|.......
E | | | | |
C | Jurassic,........|.........|.........|....Marsupials..
O | | | |
N | Triassic,........|.........|.......Birds..............
D | | |
A | Permian,.........|.........|..........................
R | | |
Y | Carboniferous,...|......Reptiles......................
|
P | |
R | Devonian,........|....................................
I | |
M | Silurian,.......Fishes................................
A |
R | Azoic.
Y |

If such discussions were not inappropriate here from their technical
character, I think I could show upon combined geological and zoological
evidence that the classes which are not present with the others at the
beginning, such as Insects among Articulates, or Reptiles, Birds, and
Mammalia among Vertebrates, are always introduced at the time when the
conditions essential to their existence are established,--as, for