32 



CENTRAL HALL. 



Lancelet. 



Bay VII. 



UolluBCB, 



by the "Wrasse, teeth are developed on the bones of the throat, 

 as well as on the bones of the jaws. Throughout this case 

 specimens, or models, of the teeth of extinct Fishes are placed 

 side by side with those of their nearest living relatives. 



The waU-case on the north side of this bay shows the 

 history of the development of various Fishes, together with the 

 form and structure of the gills, brain, heart, digestive system, 

 and other organs. 



A small case affixed to the pillar at the entrance to the fourth 

 bay illustrates the structure of the Lancelet (Branchiostoma, 

 or Amphioxus), by the aid of spirit-specimens, enlarged models, 

 and coloured diagrams. One of the most remarkable features in 

 the structure of this strange and primitive little creature is the 

 outer cavity enclosing the large and complex gullet, or pharynx. 

 The Lancelet was formerly included among the Fishes, but is 

 now accorded the rank of class (Cephalochorda) to itself 



Leaving bay VI., next the principal staircase on the east side 

 of the central hall, which, as mentioned above, is reserved for 

 recently acquired specimens of more than ordinary interest, 

 the visitor passes to bay VII. The wall-cases on both sides of 

 this bay are devoted to Molluscs, or " Shell-fish." In the first 

 division of the north wall-case is mounted a series of speci- 

 mens in spirit. 



Alongside is a large series of shells arranged on tablets to 

 show : firstly, the leading structural types, such as univalve, 

 bivalve, multivalve, &c. ; then the nature of the outer coat, 

 or " skin ; " and, thirdly, some of the more striking styles of 

 ornamentation and colouring. Following these, a division is 

 devoted to the display of the general form of the shells of 

 bivalves, especial attention being directed to the nature of 

 the hinge by which the two valves are joined. Freshwater 

 Mussels ( Unionidce) are selected as examples of great variability 

 in the form of the shell in closely allied species. Near by 

 is a small series of the shells of boring bivalves, many of them 

 in the substances they perforate. 



The left half of the wall-case on the opposite side of this bay 

 shows, in a similar manner, the varieties in form and structure 

 presented by univalve or Gastropod shells. Many of the 

 specimens have been cut to show the internal structure. 



