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, 



