2 FISH GALLERY. 



collection of skeletons of Fishes is similarly available for purposes 

 of scientific study. 



On entering the Fish Gallery from the Bird Gallery the visitor 

 will see two small Table-cases (21 and 22) standing in the middle 

 line of the Gallery, the first containing specimens and enlarged 

 models of the Lancelet, and the second containing Lampreys and 

 Hag-fishes. These are not " Fishes " in the strict use of the word. 

 The Lancelet is not even a vertebrate animal, in the sense in which 

 that term is now employed, but belongs to the Cephalochorda, a 

 division of the Chordata ranking equal with the Urochorda or 

 Tunicates (Sea-squirts, Salps, &c, exhibited in the Shell Gallery), 

 and the Vertebrata (including Lampreys, Fishes, Amphibians,, 

 Reptiles, Birds and Mammals). The Lancelet resembles the 

 Tunicates and the Vertebrates in having a median skeletal rod, 

 known as the notochord, in the dorsal position and tubular 

 character of the central nervous system, and in the perforation of 

 the side wall of the body in the neck region by gill-slits. The 

 Lancelet differs from the Tunicates and Vertebrates in that 

 the notochord extends farther forward than the central nervous 

 system. 



CEPHALOCHORDA (Lancelet). 



The Lancelet or Amphioxus (fig. 1) is a small, semitrans- 

 parent, marine animal about two inches in length (see specimens 

 in alcohol, 1046, Table-case 21) , it lives in shallow seas in many 

 parts of the world and frequently buries itself in the sand. The 

 edge of the mouth is produced into a number of curved bars or 

 "buccal cirri " (see enlarged model, 1047), which act as strainers 

 and prevent sand grains from getting into the mouth, while not 

 stopping the water that is used for respiratory purposes, nor the 

 minute living organisms that constitute the food of the Lancelet. 

 The gill-slits do not open directly on to the exterior of the body, 

 but are covered in by a wall called the atrial wall, which extends 

 as far back as the pore (atriopore), through which issues the 

 water that has passed through the gill-slits. The anus or vent is 

 unsymmetrical, being set on the left side of the lower fin ; there 

 is no distinct head, no paired fins, and no paired eyes or ears. 



