24 
CENTEAL HALL. 
Grouse and Ptarmigan in their summer dress, obtained in the 
neighbourhood of Christiania in the month of July, showing the 
general harmony of their coloration at this season to that of the 
rocks and plants among which they live. The second case 
shows the same species of animals obtained from the same spot 
in mid-winter, when the ground was completely covered with 
snow. Such complete changes as those here shown only occur 
in latitudes and localities where the differences between the 
general external conditions in the different seasons are extreme, 
where the snow completely disappears in summer and remains 
continuously on the ground during the greater part of the winter. 
Even some of the species here shown do not habitually turn 
white in the less severe winters of their southern range, as the 
Stoat in England and the Hare in Ireland. In a few permanent 
inhabitants of still more northern regions, where the snow 
remains throughout the year, as the Polar Bear, Greenland 
Falcon, and Snowy Owl (of which a specimen Is shown on the 
wing in the upper part of the winter case), the white colour is 
retained throughout the year. The whiteness of these animals 
must not be confounded with albinism (whiteness occurring 
accidentally in individuals normally of a different colour), 
illustrated in a case on the other side of the hall. 
Case iUustrat- The case nearest the great staircase contains further examples 
Ee^fmbiances^ of a subject attracting much attention among naturalists at the 
and Mimicry, present time — Protective Kesemblances and Mimicry. The 
simplest form, that of conformity of general style of colouring to 
surrounding conditions, is seen in the group at the bottom of the 
case, consisting of some of the commoner birds, mammals, and 
reptiles of the Egyptian desert, placed upon the stones and sand 
amid which they habitually live. The advantage of this colouring 
in concealing the herbivorous species from their enemies, and 
enabling the carnivorous to approach their prey unperceived, is 
obvious. Many excellent cases of concealment by adaptation to 
environment, especially in eggs and young birds, may be seen 
among the groups in the bird gallery. 
More special modifications for the same purpose are shown in 
the examples in the upper part of the case, of insects which closely 
resemble the inanimate objects, as leaves, twigs, &c., among which 
they dwell. The close imitation of a dead leaf, presented by 
