176 THE MEANING OF EVOLUTION 



the climate of any part of the Palaeozoic era. Cer- 

 tainly of the climate earlier than the Carboniferous it 

 is very risky to say anything definite. 



The forests of the coal period seem actually to 

 have cleared the air; at least now we begin to find 

 creatures related to our salamanders and frogs moving 

 about among the stumps of the marshes. These am- 

 phibians are evidently the descendants of some of the 

 fishes of the Devonian times. Among these fishes 

 were some which bear a great resemblance to a few 

 found in South America, in Africa and Australia to- 

 day, and which we know as lungfish. Anyone who 

 has cleaned our fresh water fishes in preparation for 

 the table will remember that inside of them there is a 

 long slender bladder filled with air. This bladder 

 assists in making the fish light, hence making it easier 

 for it to support itself in the water. In certain- 

 swampy regions these lungfish swim freely in the 

 water of the marshes. When the dry season comes, 

 however, the water evaporates, draining the marshes 

 completely. This would prove the death of most 

 fishes. The lungfish have a curious habit which keeps 

 them over the dry season. They cover themselves 

 with a coat of mud, inside of which there is a lining 

 of slime produced from their bodies. In such cocoon- 

 like cases they survive the drought. The means by 

 which they breathe during this dry season is inter- 



