172 THE HAUNTS OF LIFE 
they live chiefly on herring, mackerel, etc., 
makes them grow very rapidly, and those that 
ascend the rivers as “‘grilse” the following 
year are often more than double that length. 
Many of them, however, spend two or three or 
more years in the sea before they return, and 
these grow to a great size. Some do not return 
at all, but remain about the estuaries. It is un- 
likely that those that do this ever breed ; spawn- 
ing is only known to take place in fresh water. 
THE STORY OF THE LAMPREY 
One of the most interesting animals that 
live in fresh-running water is the lamprey. 
It is not very easy to see, for most of its life 
is spent concealed in the sand. But at the 
breeding season it comes out of its hiding- 
place, and begins to make preparations for 
the advent of the next generation. 
Let us look for a moment at the lamprey 
itself. The common brook-lamprey is eel-like 
in appearance, and, when full grown, is about 
7 inches long. Its skeleton is gristly instead 
of bony, like that of the true fishes. It has 
two fins on the middle line of the back and a 
tail-fin, but no paired fins. It has no jaws, 
