252 The Study of Animal Life PART in 



and multiply. Unpleasant to taste, they are left in peace, though 

 a crab sometimes cuts a tunic off as a cloak for himself. 



3- The Lancelet. The lancelet (Amphioxus] is a simple 

 Vertebrate, far below the structural rank of fishes. It is only 

 about 2 inches in length, and, as both English and Greek names 

 suggest, it is pointed at both ends. On the sandy coasts of warm 

 and temperate seas it is widely distributed. 



From tip to tail of the translucent body runs a supporting noto- 

 chord ; above this is a spinal cord, with hardly a hint of brain. 

 The pharynx bears a hundred or so gill-slits, which in the adult 

 are covered over by folds of skin, so that the water which enters 

 by the mouth finds its way out by a single posterior aperture. 

 Although Amphioxus has no skull, nor jaws, nor brain, nor limbs, 

 it deserves its position near the base of the Vertebrate series. The 

 sexes are separate, and the eggs are fertilised outside of the body. 

 The development of the embryo has been very carefully studied, 

 and is for a time very like that of Tunicates. 



4- Round-Mouths or Cyclostomata. The hag -fishes and 



the lampreys and a few allied genera must be excluded from the 

 class of fishes. They are survivors of a more primitive race. 

 They are jawless, limbless, scaleless, and therefore not fishes. 



The lampreys (Petromyzon} live in rivers and estuaries, and also 

 in the wider sea. They are eel-like, slimy animals. The skeleton 

 is gristly ; the simple brain is imperfectly roofed ; the single nostril 

 does not open into the mouth ; the rounded mouth has horny teeth 

 on the lips and on the piston-like tongue ; there are seven pairs of 

 gill-pouches which open directly to the exterior and internally into 

 a tube lying beneath and communicating with the adult gullet ; the 

 young are blind and otherwise different from the parents, and may 

 remain so for two or three years. 



Though lampreys eat worms and other small fry, and even dead 

 animals, they fix themselves aggressively to fishes, rasping holes 

 in the skin, and sucking the flesh and juices. They also cling to 

 stones, as the name Petromyzon suggests. 



Some species drag stones into a kind of nest. They spawn in 

 spring, usually far up rivers, for at least some of the marine 

 lampreys leave the sea at the time of breeding. The young are in 

 many ways different from the parents, and that of the small river 

 lampern (Petromyzon branchialis] used to be regarded as a distinct 

 animal Ammoccetes. The metamorphosis was discovered two 

 hundred years ago by Baldner, a Strasburg fisherman, but was 

 overlooked till the strange story was worked out in 1856 by 

 August Miiller. Country boys often call the young " nine-eyes," 

 miscounting the gill apertures, and the Germans also speak of 

 neun-augen. 



