xxviii ILLUSTRATIONS 



FIG. PAGE 



25. Worms, Middle Cambrian and recent . 128 



26. Chaetognaths, Cambrian and recent . 129 



27. Jellyfish, Cambrian and recent 130 



28. The twelve chief habitat zones 131 



29. Life zones of Cambrian and recent invertebrates 131 



30. Map — North America in Cambrian times 132 



31. Sea-scorpions of Silurian times 133 



32. Map — North America in Middle Devonian times 134 



2$. Changing environment during fifty million years 135 



34. Fossil starfishes 136 



35. Mutations of Waagen in ammonites 139 



36. Mutations of Spirifer mucronatus 140 



37. Shell pattern and tooth pattern of Glyptodon 148 



38. Teeth of Euprotogonia and Mcniscotherium 149 



39. Adaptation of the fingers in a lemur 150 



40. Total geologic time scale 153 



41. Adaptation of form in three marine vertebrates — shark, ichthyosaur, 



and dolphin 155 



42. Chronologic chart of vertebrate succession 161 



43. The existing lancelets (Amphioxus) 162 



44. Five types of body form in fishes 163 



45. Map — North America in Upper Silurian time 164 



46. The Ostracoderm Palcraspis 165 



47. The Antiarchi. Bothriolepis 165 



48. The Arthrodira. Dinichthys intermedius 166 



49. A primitive Devonian shark, Cladoselache 167 



50. Adaptive radiation of the fishes 168 



51. Fish types from the Old Red Sandstone 170 



52. Map — the world in Early Lower Devonian times 171 



53. Change of adaptation in the limbs of vertebrates 172 



