x Contents 



CHAPTER V. 



MORPHOLOGY OF THE FINS OF FISHES. 



PAGE 



Origin of the Fins of Fishes. Origin of the Paired Fins. Development of the 

 Paired Fins in the Embryo. Evidences of Palaeontology. Current The- 

 ories as to Origin of Paired Fin. Balfour's Theory of the Lateral Fold. 

 Objections. Objections to Gegenbaur's Theory. Kerr's Theory of Modi- 

 fied External Gills. Uncertain Conclusions. Forms of the Tail in Fishes. 

 Homo logics of the Pectoral Limb. The Girdle in Fishes other than 

 Dipnoans 62 



CHAPTER VI. 



THE ORGANS OF RESPIRATION. 



How Fishes Breathe. The Gill Structures. The Air-bladder. Origin of the 

 Air-bladder. The Origin of Lungs. The Heart of the Fish. The Flow 

 of Blood 91 



CHAPTER VII. 



THE NERVOUS SYSTEM. 



The Nervous System. The Brain of the Fish. The Pineal Organ. The 

 Brain of Primitive Fishes. The Spinal Cord. The Nerves 109 



CHAPTER VIII. 



THE ORGANS OF SENSE. 



The Organs of Smell. The Organs of Sight. The Organs of Hearing. 

 Voices of Fishes. The Sense of Taste. The Sense of Touch 115 



CHAPTER IX. 



THE ORGANS OF REPRODUCTION. 



The Germ-cells. The Eggs of Fishes. Protection of the Eggs. Sexual Modi- 

 fication 124 



CHAPTER X. 

 THE EMBRYOLOGY AND GROWTH OF FISHES. 



Postembryonic Development. General Laws of Development. The Signifi- 

 cance of Facts of Development. The Development of the Bony Fishes. 

 The Larval Development of Fishes. Peculiar Larval Forms. The Devel- 

 opment of Flounders. Hybridism. The Age of Fishes. Tenacity of 



