LOWEST VERTEBRATES. 247 



Having attached itself to a stone of a suitable size, the 

 creature swims to the place selected, supporting the 

 weight with infinite skill until the moment when it 

 suddenly drops it into the muddy bed of the stream. 

 Then the stone is worked backwards and forwards for 

 some hours, the discolouration of the water serving to 

 reveal the presence of the Lamprey from the bank. After 

 the task has been accomplished by these incessant 

 efforts, a suitable excavation remains for the deposition 

 of the eggs in the required position. The mouth of the 

 Lamprey during the alternations of expansion and contrac- 

 tion is a truly formidable looking cavity. A freshly caught 

 and still living specimen has the power of emitting a 

 strange hissing sound which is doubtless due to the con- 

 traction of the sucker-mouth. The Sea Lamprey 

 sometimes falls a prey to the attacks of numerous parasitic 

 leeches adherent to its body by means of suckers a 

 curious case of retributive justice, since the Lamprey is 

 itself parasitic on Fishes. 



Lampern, or River Lamprey. Local name, Seven eyes, 

 P. fluviatilis. in allusion to the seven gill-slits. Dis- 



tinguished from the last by its smaller 

 size never over fifteen inches greenish-blue colour, and 

 the absence of mottling. It is common in our Shropshire 

 streams, where bunches of eighteen or twenty may often 

 be seen lying in holes in the gravelly bottoms, which it 

 prefers for spawning. This used to be considered a 

 purely freshwater form, but has been taken in the sea, 

 and is now known to migrate in the same way as the 

 Sea Lamprey. The young are believed to pass through 

 their metamorphoses and reside in fresh water for three 

 or four years. 



