55. The same, modified for a bird 151

56. The same, modified for a mammal 151

57. A series of embryos at three comparable and progressive
stages of development, representing each of the classes of
vertebrated animals below the Mammalia 152

58. Another series of embryos, also at three comparable and
progressive stages of development, representing four different
divisions of the class Mammalia 153

59. Diagram of geological succession of the classes of the Animal
Kingdom 165

60. Skull of _Oreodon Culbertsoni_ 167

61,62. Horns of _Cervus dicrocerus_ 168

63. Horns of _C. matheronis_ 168

64. Horns of _C. pardinensis_ 168

65. Horns of _C. issiodorensis_ 168

66. Horns of _C. Sedgwickii_ 168

67. Successive stages in the development of an existing Deer's
Antlers 169

68. Homocercal tail 169

69. Heterocercal tail 170

70. Vertebrated but symmetrical fin (diphycercal) 170

71. Tail of _Archaeopteryx_ 171

72. Tail of modern Bird 171

73. _Archaeopteryx macura_, restored 172

74. Skeleton of Polar Bear 174

75. Skeleton of Lion 175

76. Anterior limb of Man, Dog, Hog, Sheep, and Horse 176

77. Posterior limb of Man, Monkey, Dog, Sheep, and Horse 177

78. Posterior limb of _Baptanodon discus_, and anterior limb of
_Chelydra serpentina_ 179

79. Paddle of a Whale 180

80. Fossil skeleton of _Phenacodus primaevus_ 184

81. Bones of the foot of four different forms of the perissodactyl
type