40 LAND LIFE BEGINS 



and centipedes. All these developed gradually in the 

 age I am discussing. 



But I am hurrying over these lowly creatures in 

 order to give more time to a more important invader 

 of the land. This was the fish. You may think it 

 easy enough to imagine snails and worms being 

 adapted to life on land, but the idea of a branch of 

 the fishes leaving the water and becoming land ani- 

 mals must seem strange to those who have not a 

 good knowledge of natural history. If it be clearly 

 understood that, as I have so often said, these changes 

 and adaptations to a new life were very slow and 

 gradual, the difficulty lessens. But it disappears 

 altogether when you take a good work on natural 

 history and zoology, and read what the author has to 

 say about "lung-fishes." 



He will tell you that in certain rivers of Queensland 

 there are short, stumpy fishes which have a lung as 

 well as gills. The water of those rivers runs low in 

 the summer, and the lung then comes into play to 

 help out the animal's breathing. You v/ill next learn 

 that in certain rivers of Egypt and of South America 

 there are fishes of the same family with two lungs 

 (like ourselves) as well as gills. The rivers in which 

 they live dry up entirely in the summer. The gills 

 (for breathing in water) are then useless. The fishes 

 bury themselves in the dry mud, and breathe by 

 their lungs until the waters flow once more. They 

 can walk on their fins; and, in fact, the fins of some 



