174 



THE ORIGIN AND EVOLUTION OF LIFE 



It is through the discovery of primitive types of the fringe- 

 finned ganoids, to which Huxley gave the appropriate name 

 Crossopterygia, in reference to the fringe of dermal rays around 

 a central lobe-iin of cartilaginous rods, that the true ancestry 

 of the Amphibia and of the amphibian limb has been traced. 

 This is now regarded as due to a partial change of adaptation, 



Fig. 55- Phosphorescent Illuminating Organs. 



The abyssal fishes represented in Fig. 54 as they are supposed to appear in the darkness 

 of the ocean depths. .A.fter models in the American Museum of Natural History. 



incident to the passage of the animal from the littoral life zone 

 to the shore zone, whereby the propelling fin was gradually 

 transformed into the propelling limb. This transformation 

 implies a long terrestrio-aquatic phase, in which the fin was 

 partly used for propulsion on muddy surfaces (Fig. 53). 



In the reversed parallel retrogressive evolution of the lung- 

 fishes {Lepidosiren, Gymnotus), of the fringe-finned fishes {Cala- 

 moichthys) and of the bony fishes {Angicilla), the final eel-shaped. 



