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! 
Fic. 15. —THE QUEENSLAND Mup-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- 
