142 THE HAUNTS OF LIFE 
its ancestors were deep-water fishes. Similarly, 
though the flounder is often found in rivers 
20 miles from the sea, it does not spawn in 
fresh water, it must go back to its old home in 
the shallow sea. It will be interesting to think 
out some cases that seem to break this rule. 
It is also to be remembered that some ani- 
mals are at present making the transition from 
salt water to fresh. The flounder is a case in 
point, undoubtedly a marine fish, but be- 
coming more and more accustomed to the 
rivers. The quaint Manatee, included with 
the Dugong in the small order of mammals, 
known as sea-cows, or Sirenia, is typically a 
coastal mammal, but it goes far up the rivers, 
and it is now found, for instance, in the Ever- 
glades of Florida, a far cry from the sea. 
In any case we should not think of the 
fresh-water fauna as a fixed and finished as- 
semblage of animals. It is a noteworthy fact 
that many fresh-water animals spend only a 
part of their lives in the fresh water. Some 
of these seem to be still in process of accus- 
toming themselves to it, others to be leaving 
it for salt water, and others again are appar- 
ently on the way to becoming land animals. 
How can we tell in which direction a par- 
