xiv Contents 



CHAPTER XXIV. 



THE EVOLUTION OF FISHES. 



PAGE 



The Geological Distribution of Fishes. The Earliest Sharks. Devonian 

 Fishes. Carboniferous Fishes. Mesozoic Fishes. Tertiary Fishes. Fac- 

 tors of Extinction. Fossilization of a Fish. The Earliest Fishes. The 

 Cyclostomes. The Ostracophores. The Arthrodires. The Sharks. 

 Origin of the Shark. The Chimaeras. The Dipnoans. The Crossopte- 

 rygians. The Actinopteri. The Bony Fishes 435 



CHAPTER XXV. 



THE PROTOCHORDATA. 



The Chordate Animals. The Protochordates. Other Terms Used in Classifi- 

 cation. The Enteropneusta. Classification of Enteropneusta. Family 

 Harrimaniidae. Balanoglossidae. Low Organization of Harrimaniidae 460 



CHAPTER XXVI. 

 THE TUNICATES, OR ASCIDIANS. 



Structure of Tunicates. Development of Tunicates. Reproduction of Tuni- 

 cates. Habits of Tunicates. Larvacea. Ascidiacea. Thaliacea. Origin 

 of Tunicates. Degeneration of Tunicates 467 



CHAPTER XXVII. 

 THE LEPTOCARDII, OR LANCELETS. 



The Lancelet. Habits of Lancelets. Species of Lancelets. Origin of Lance- 

 lets 482 



CHAPTER XXVIII. 

 THE CYCLOSTOMES, OR LAMPREYS. 



The Lampreys. Structure of the Lamprey. Supposed Extinct Cyclostomes. 

 Conodontes. Orders of Cyclostomes. The Hyperotreta, or Hagfishes. 

 The Hyperoartia, or Lampreys. Food of Lampreys. Metamorphosis of 

 Lampreys. Mischief Done by Lampreys. Migration or "Running" of 

 Lampreys. Requisite Conditions for Spawning with Lampreys. The 

 Spawning Process with Lampreys. What Becomes of Lampreys after 

 Spawning ? 486 



