The Archeopteryx (_from Professor Owen's "Anatomy of Vertebrata"_) ... 73, 132 {xiv} Cuttle-Fish ... 75, 141 Skeleton of Ichthyosaurus ... 78, 107, 132, 177 Cytheridea Torosa (_from Messrs. Brady and Robertson's paper in Ann. and Mag. of Nat. Hist., 1870_) ... 79 A Polyzoon, with Bird's-head processes ... 80 Bird's-head processes greatly enlarged ... 81 Antechimis Minutissimus and Mus Delicatulus (_from Mr. Andrew Murray's "Geographical Distribution of Mammals"_) ... 82 Outlines of Wings of Butterflies of Celebes compared with those of allied species elsewhere ... 86 Great Shielded Grasshopper ... 89 The Six-shafted Bird of Paradise ... 90 The Long-tailed Bird of Paradise ... 91 The Red Bird of Paradise ... 92 Horned Flies ... 93 The Magnificent Bird of Paradise ... 93 _(The above seven figures are from Mr. A. Wallace's "Malay Archipelago"_) Much enlarged horizontal Section of the Tooth of a Labyrinthodon (_from Professor Owen's "Odontography"_) ... 104 Hand of the Potto (_from life_) ... 105 Skeleton of Plesiosaurus ... 106, 133 The Aye-Aye (_from Trans, of Zool. Soc._) ... 108 Dentition of Sabre-toothed Tiger (_from Professor Owen's "Odontography"_) ... 110 Trilobite ... 135, 171 Inner side of Lower Jaw of Pleurodont Lizard (_from Professor Owen's "Odontography"_) ... 148 Solenodon (_from Berlin Trans._) ... 149 Tarsal Bones of Galago and Cheirogaleus (_from Proc. Zool. Soc._) ... 159 Squilla ... 160 Parts of the Skeleton of the Lobster ... 161 [Page xv] Spine of Galago Allenii (_from Proc. Zool. Soc._) ... 162 Vertebrae of Axolotl (_from Proc. Zool. Soc._) ... 165 Annelid undergoing spontaneous fission ... 169, 211 Aard-Vark (_Orycteropus capensis_) ... 174 Pangolin (_Manis_) ... 175 Skeleton of Manus and Pes of a Tailed Batrachian (_from Professor Gegenbaur's "Tarsus and Carpus"_) ... 178 Flexor Muscles of Hand of Nycticetus (_from Proc. Zool. Soc._) ... 180 The Fibres of Corti ... 279 {1} * * * * * THE GENESIS OF SPECIES. CHAPTER I. _INTRODUCTORY._