lum grows over the aperture of the gills, closing it, and the tadpole becomes a frog, breathing air by means of lungs. The tail, moreover, has disappeared and limbs are developed.
This is a new mode of progression, and excepting in the snake and whale, the hind limbs in all animals above fish, are employed as a means of locomotion. In the frog and the majority of the other vertebrates the fore limbs serve the same function, but in the whale they are modified to flippers, in birds to wings, and in man to arms.
Reptiles are represented at the southern end by alligators and crocodiles. Above these exhibits is a very instructive set of longitudinal sections of the skulls of different animals, showing the development of the brain. It will be seen that the brain, coming forward, causes the jaw-bones to be less prominent in man than in any other animal.
At the top of the staircase is a very rare specimen, the great ribbon-fish, an inhabitant of the deep sea, and like the frost-fish, only obtainable when by some extraordinary circumstance, it is cast up upon the shore. The skeleton has been removed from the body, and is shown above it in a good state of preservation. The skin has been stuffed, and its delicate markings and colouring have been renovated and rendered permanent. This was necessary, as fish which live deep down under a high pressure, are very liable, on coming to the surface, to fall to pieces, and lose their brilliancy in a remarkably short time.
In the upper gallery, the wall-cases are occupied by the very large class of birds, which undoubtedly form a fine display. Nests containing eggs are exhibited in many instances, and offer an additional attraction.
Birds are the best marked group of vertebrata; they have no intimate connection with other groups, and are readily recognisable. The presence of feathers, together with the fact that by means of the large air-sacs in connection with the lungs, and the porous nature of the bones, the air in respiration finds easy access to all parts of the body, causes the blood supplied by a very large heart, to be maintained at a temperature higher than in any other animal. This, with the peculiar differentiation of the fore-limbs into wings, enables the bird to support itself in flight.
