The Structure of Game Fishes II 
jority separate. Many young of pelagic fishes 
attach themselves to large jellyfishes; others to 
the physalia, and some adults enter the intestinal 
tube of holothurians. 
There are two other methods of reproduction 
among fishes and the fishlike animals. In some, 
as the surf-fishes and certain sharks, the young 
are born alive. The young of twenty or thirty 
or more surf-fishes school and swim together. 
Other fishes are ovoviviparous, the eggs being 
retained in the body until the young are hatched. 
In the vast concourse of fishes of the world 
every possible habit is seen. Originally all were 
doubtless salt-water forms, but they have entered 
rivers and streams, and in time have become 
adapted to their environment. Some fishes, 
like the salmon, enter fresh water to spawn. 
Others, like the eel, seem to reverse this. Cer- 
tain fishes hibernate when water disappears. 
Others cross overland to reach water, while 
the strange periophthalmus and another genus 
leave the water and wander along the shore in 
search of food. 
The fishes are found at various depths of 
the ocean, some at a depth of several miles 
being blind. Those living in these abysmal 
