More special modifications for the same purpose are shown in the adjacent bay on the east side of the hall by Insects which closely resemble the objects, such as leaves, twigs, etc., among which they dwell. The close imitation of a dead leaf, presented by the Leaf-Butterfly (_Callima inachis_), when its wings are closed, could not be surpassed. In a further stage of the same condition, called “Mimicry,” the object resembled, or mimicked, is another living animal, belonging to a different species, family, or even order. The resemblance in these instances is also believed to be for protection, or to be in some way advantageous to the animal in which it occurs. We know, however, so little of the habits and life-history of animals in a state of nature that many of the purposes supposed to be served by particular colours or appearances can only be regarded at present as conjectural. Whatever be the real explanation, the facts shown by the specimens in this bay are very curious, and worthy of careful consideration. [Sidenote: Group illustrating Albinism.] The next case on the east side of the middle of the hall contains a series of specimens illustrating _albinism_, a condition in which the pigment, or colouring matter, usually present in the skin, hair, or feathers, and giving the characteristic hue, is absent. Individuals in this condition occur among many animals of various kinds, and are called “_albinos_.” In some of the specimens shown in the case the albinism is complete, but in many it is partial, the absence of colouring matter being limited to certain portions of the surface. Other examples of complete or partial albinism are shown in the North Hall. [Illustration: FIG. 1.--THE LEAF-BUTTERFLY (_Callima inachis_) IN FLIGHT AND AT REST.] [Sidenote: Group illustrating Melanism.] The adjacent case shows examples of the opposite condition called _melanism_, depending upon an excess of dark colouring matter or pigment in the skin and its appendages, such as hair, feathers, etc., beyond what is commonly met with in the species. This is by no means so frequent as albinism. A black Leopard in the middle of the case is a good illustration. This is not a distinct species, but merely an individual variety of the common Leopard, born from parents of the normal colour. A black Bullfinch is introduced as an example of acquired melanism, this bird having turned black in captivity. [Illustration: FIG. 2.--THE SOMALI TSETSE-FLY (_Glossina longipennis_). Enlarged 4 diameters. Shows the complete closure of the wings in the resting position, and the prominent proboscis, characteristic of the genus.] [Sidenote: Group illustrating Intermediate Forms in Nature.]