THE FRESH WATERS 173 



but it has a round sucker-mouth, and a very 

 muscular tongue, covered with horny teeth. 

 With its sucker-mouth it fastens itself to the 

 body of a fish, and, protruding its rough 

 tongue, proceeds to rasp the flesh off its un- 

 fortunate victim. Fishes have sometimes been 

 seen to turn over on their sides, so that the 

 troublesome "boarder" is out of water, and 

 is forced to let go its hold. 



Along each side of the body of the lamprey, 

 near the head, there are seven conspicuous 

 holes. These are the gill-slits, and the gills 

 to which they lead are continually washed by 

 water. In most fishes, water enters by the 

 mouth and flows out at the gill-slits, carrying 

 away the used air from the blood. But the 

 lamprey uses its mouth to fasten itself to its 

 prey, and, in its case, water flows in at the 

 gill-slits and out again. 



The eyes are large, and there is a single 

 nostril, which lies right in the middle line of 

 the head so that, whichever side of the body 

 we look at, we see an eye and eight holes. 

 This is why lampreys are popularly called 

 "nine-eyes" or "niners." 



As spawning-time approaches, the lampreys, 

 both male and female, set about preparing a 



