THE FRESH WATERS 155 



hardens, and the fish lies safely within it until 

 the rainy season comes, and the lake is once 

 more filled with water. Specimens have been 

 brought to this country within their mud-nests, 

 and they sometimes come out all right, even 

 after they have been out of the water for nine 

 months. A fish out of water indeed ! 



FIG. 15. THE QUEENSLAND MUD-FISH (NEOCERATODUS). 

 Breathing by Lungs as well as by Gills. 



THE DANGER OF FROST 



In many parts of the world one of the severest 

 trials of life is the freezing of the water. Even 

 a resourceful animal, like an otter, may be 

 starved, because the water is frozen, or it may 

 venture through a hole in the ice and fail to 

 find its way back again. Many small fresh- 

 water animals die altogether in the winter, and 

 only their eggs live on, protected within hard 

 envelopes. The fresh-water sponge on the 

 stones of the river and lake dies away, and in 

 the late autumn it looks as if it were rotten. 



