438 THE LOWEST VERTEBKATES. 



practically blind. The members of this group have seven 

 gill-slits ; and the mouth, a mere slit when closed, opens 

 as a circular orifice, having suctorial lips and a flexible 

 disc. This lamprey is much esteemed as food, and is 

 caught in wicker baskets specially constructed and placed 

 in the mud. Like the rest, it is carnivorous, rasping the 

 sides of living fishes, to which it adheres for the purpose, 

 with its hard teeth. It enters English rivers to spawn in 

 the spring. 



The commoner Lampern was till recently regarded as a 

 fresh -water form, but later investigations have estab- 

 tLam ern Wished its presence in the sea, and it is now 

 or River- regarded, like the last, as an anadromous 

 Lamprey. fQj,^^^ j^ difi'ers in its smaller size, rarely 

 exceeding a length of 15 inches, as well as in the bluish 

 colour and absence of spots. It spawns in rivers hav- 

 ing a stony bed, the eggs being deposited in furrows 

 excavated by the lamj^erns themselves ; and it is thought 

 to die after spawning. Its food consists of the flesh of 

 living and dead fish, worms, and insects. Its chief use is 

 as bait in the cod-fishery. 



The smallest of the three, the Mud-Lamprey, familiarly 

 known as the "Pride," does not exceed a length of 10 

 t Mud- inches. Like the last, it is, chiefly on account 



Lamprey, ^f [^^ toughness, an excellent bait for some 

 sea-fish. Beyond its supposed residence in salt water and 

 invariable ascent of rivers for spawning, after which or- 

 deal it is supposed to die, little has been recorded of the 

 life-history of this form, the most interesting discovery 

 being that of its larva, which was long regarded as a 

 distinct species. 



2. The Hag-Fish. 



In the singular Hag-fish we have a true parasite, for the 

 "Borer," as it is called, is most commonly taken from the 



