72 



THE DOCTRINE OF DESCENT. 



the tail and renders it strikingly unsymmetrical. The 

 Ganoids are, as comparative anatomy has proved with 



certainty, a development of the shark-like fishes, if not 

 decidedly of a higher grade. The Ganoids, therefore, 

 presuppose the shark. 



The carboniferous period owes its name to the enor- 

 mous accumulation occurring in its midst, of the re- 

 mains of terrestrial plants, fern-like Calamites, and 

 more especially of Sigillaria and Lepidodendra, stand- 

 ing between vascular Cryptogams and Conifers. They 

 formed tropical bog-forests, such as Franz Unger some 

 years ago attempted to restore in an ingenious compo- 

 sition. In these steaming primaeval forests, diflfering 

 from the early beginnings of antecedent periods by 

 their extent and luxuriance, new phases of animal 

 life become manifest — scorpions, myriapods, and in- 

 sects — in other words, air-breathing Articulata, and 

 likewise the first air-breathing Vertebrata. The latter, 

 the Cheirotheria, or Labyrinthodonta (colossal Batra- 

 chians) possess pre-eminently amphibian characters, and 

 exhibit, for example, several important characteristics of 

 the Batrachian skull, whereas their skin-covering recalls 



