THE FRESH walieRS 145 
flies, whose larve live in the fresh waters. But 
no one can suppose that these insects, or any 
insects, had their original home in water. The 
explanation is that when an animal lives in a 
haunt full of dangers for the young, it has often 
circumvented the difficulty by finding another 
haunt for the juvenile stages. The aquatic 
larve of insects are not old fashioned; they 
show new-fashioned fitnesses to a haunt which 
is really rather foreign to the insect’s nature. 
CIRCULATION OF MATTER IN THE 
FRESH WATERS 
To understand the animal life of a lake or 
pond we must as usual start with the plants. 
For the plants, which are able to feed upon 
the not-living, supply food for the animals 
which feed upon the living, or what has been 
living, or what has been made by something 
living. There are many fresh-water plants 
growing round the margin, like bog-bean, 
mare’s tail, iris, and bullrush; others, like 
water-lilies, are rooted at a considerable depth, 
and send their leaves and flowers on long 
stalks up to the surface; others, like duck- 
weed, with roots, and bladderwort, without 
