Illustrations 



Convergence of form in shark, ichthyosaur, and porpoise 



. . . . Frontispiece 



1 Swimming principles of vertebrates 14 



2 Swimming movements of eel and fusiform nsh . . . 17 



3 Some of the smaller aquatic mammals 27 



4 The insectivore otter Potomogale 29 



5 ' Pinniped postures 34 



6 Sirenians 39 



7 Body postures of the manati . . . . . .45 



8 Facial postures of the manati . 46 



9 Types of the larger whales 50 



10 Heads of porpoises 55 



11 Some extinct, aquatic reptiles . . . . . . . 59 



1 2 Pharyngeal region of Kogia 89 



13 Blow-holes of whalebone and toothed whales . . . 93 



14 Skeletons of pinnipeds 94 



15 Blow-hole action in a porpoise 98 



16 Skulls of sirenians 109 



17 Skull of a toothed whale 116 



18 Skull of the sperm whale 124 



19 Skull of a whalebone whale . 128 



20 Skull of the right whale 135 



21 Extremes of cetacean neck vertebrae 149 



22 Dorsal musculature of a sea-lion 158 



23 Dorsal musculature of a seal 159 



24 Ventral musculature of a sea-lion 162 



25 Ventral musculature of a seal 163 



26 Panniculus carnosus musculature of aquatic mammals . .167 



27 Lateral musculature of the narwhal 169 



28 Skeletons of toothed whales 171 



29 Skeletons of zeuglodonts 175 



30 Vertebrae of a porpoise .179 



31 Sterna of whales and sirenians 181 



32 Development of the cetacean flukes 198 



33 Caudal restorations of ichthyosaurs 203 



34 Pectoral limb bones of some aquatic reptiles . . . .211 



35 Pectoral limb bones of pinnipeds and sirenians . . . 217 



