xvi CONTENTS 



another, and the organ may undergo structural modification in 

 consequence. Examples of change of function : the wing of the 

 bat ; lungs and swimming bladders ; electric organs of fish. 



Other Objections. Insufficiency of Time. Evidence of Design and 

 Forethought. Instinct. 



LECTURE VII. (Pp. 173-199.) 



THE ORIGIN OF VERTEBRATED AMIMALS. 



The evidence available for the determination of genetic affinities is 

 of three chief kinds : — 



1. That afforded by comparison of structure. 



2. That afforded by development. 



3. That afforded by fossils. 



THE CRANIATE VERTEBRATES. 



The Zoological characters of the higher Vertebrates. The brain 

 and spinal cord ; the vertebral column and skull. 



The characters of Fish and Amphibians. The mutual relations of 

 the two groups. The transition from the water -breathing to 

 the air-breathing condition. The evolution of lungs. 



The Zoological characters of Reptiles, Birds, and Mammals. The 

 relations of these groups to Fish and Amphibians. Evidence 

 in favour of the descent of Reptiles, Birds, and Mammals from 

 aquatic ancestors. 



The mutual relations of Reptiles and Birds. The special characters 

 of Birds. Fossil forms intermediate between the two groups. 

 Embryological evidence. The development of the pelvic girdle. 



The special characters of Mammals. The development of Mammals. 

 Indications of the former presence of large eggs. The eggs of 

 Echidna. Palasontological evidence in favour of the descent of 

 Mammals from Reptiles. 



THE ACRANIATE VERTEBRATES. 

 The Anatomical and Embrylogical characters of Amphioxus. Re- 

 lation of Amphioxus to other Vertebrates. 



The characters of Ascidians. Supposed ancestral relations to other 

 Vertebrates. The development of Ascidians. Evidence of 

 degeneration. Evidence in favour of a pelagic marine ancestry 

 for all Vertebrates. Supposed relations with Invertebrates. 



