32 
CENTEAL HALL. 
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 wall-case on the north sid^e 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. 
Lancelet. A small case affixed to the pillar at the entrance to the fourth 
bay illustrates the structure of the Lancelet {Brancliiostoma, 
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. 
Bay VII. Leaving bay VL, next the principal staircase on the east side 
Molluscs. ^£ ^YiQ 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. 1^^'ear 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. 
