A MOUNTAIN STREAM 165 



preys. We found about twenty in a backwater pool, 

 in what was really part of the flood-bed of the stream. 

 They were the young of the Brook Lamprey (Lam- 

 petra planeri), and there are two other kinds in the 

 river the Sea Lamprey (Petromyzon marinus), which 

 usually goes down to the sea, and the River Lamprey 

 (Lampetra fluviatilis), which sometimes goes down to 

 the sea. The spawning of all the three kinds occurs 

 about midsummer, and the sticky eggs are laid in a 

 nest of stones which saves them from being washed 

 downstream. The young ones are quickly hatched 

 and they seek out places where the water flows slowly 

 and where there is an abundance of minute aquatic 

 creatures which are swept through a sieve into the 

 toothless, horseshoe-shaped mouth. They are curious 

 old-fashioned creatures, with hidden and rudimentary 

 eyes, with seven small gill openings in a groove, and 

 an unpaired nostril high up on the top of their head. 

 They remain young for three or four years and then 

 change into Lampreys; the mouth becomes circular 

 and abundantly furnished with horny teeth; the eyes 

 develop and there are remarkable internal changes. 

 They fasten themselves to fishes, taking a very firm 

 grip and using a toothed muscular piston, which we 

 can hardly call a tongue, to rasp a hole through the 

 skin. One must admit that if the word "fish" is to 

 mean anything precise, we must not call Lampreys 

 fishes. They are jawless, limbless, and scaleless, their 

 gills are in peculiar pockets, and their unpaired nostril 

 is altogether peculiar. In fact, they belong to a class 

 of Round Mouths, or Cyclostomes, which also includes 

 the Glutinous Hag (Myxine) of the sea. Almost the 

 only feature that they have in common with Eels is 



