LIST OF ILLUSTRATIONS xxi 



FACING PAGE 



The Evolution of the Paddle of the Penguin - . . . 385 



After Pycraft. 

 Section of the Head of the Helmet Hornbill, showing the 



Dense Layer of Horn and Bony Tissue forming the Casque 422 

 From a Specimen in the British Museum. 

 The Trunk Skeletons of Chionis, the Diving Petrel and the 



Fork-tailed Petrel ..---..-. 451 



From Specimens in the British Museum of Natural History. 



The Trunk Skeletons of the Guillemot and Diver, showing 



Modifications Induced by Diving-habits . . . . . ^gj 

 From Specimens in the British Museum of Natural History. 



Shank of the Leg of the Red-throated Diver and of the Great 



Crested Grebe . . 452 



From Specimens in the British Museum of Natural History, 



