THE FRESH WATERS 155 



and 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 se- 

 verest 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 rot- 



