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 
