INTRODUCTORY COLLECTION. 
25 
Individuals in this condition occur among many animals of 
various kinds, and are called " albinos." In some of the speci- 
mens shown in the case the albinism is complete, but in many 
it is partial, the absence of colouring matter being limited to 
portions of the surface only. 
A fourth case shows examples of the opposite condition, Group illus- 
•called melanism, depending upon an excess of dark-coloured ^el^sm. 
pigment in the skin and its appendages, the hair, feathers, etc., 
beyond what is normally 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. It is not a distinct 
.-species, but an individual variety of the common Leopard, born 
from parents of the normal colour. A black Bullfinch is intro- 
duced as an example of acquired melanism, the bird having 
turned black in captivity. 
The bays or alcoves round the hall, five on each side, are Bays or 
devoted to the Introductory or Elementary Morphological Col- HalL 
lection, designed to teach the most important points in the 
structure of the principal types of animal and plant life, and 
the terms used in describing them, all which should be known 
before the systematic portion of the collection can be studied 
with advantage. This has been called the " Index Museum," 
as it was thought at one time that it would form a sort of 
epitome or index of the main collections in the galleries ; but 
the name does not exactly express what it has developed into. 
It is really more like the general introduction, which almost 
always precedes the systematic portion of treatises on any 
branch of natural history. As mentioned before (p. 19), this 
collection is at present far from complete ; in fact, only in its 
infancy ; and as nothing exactly like it has been exhibited in 
any public museum before, it may, as its formation goes on, be 
subject to much modification and improvement ; but it is hoped 
that it may ultimately serve as a guide for the formation of 
educational biological museums elsewhere. The space being 
strictly limited, the number of illustrative specimens is neces- 
sarily restricted, probably to the advantage of the student, at 
all events in the earlier part of his career. In examining this 
collection the visitor should follow each case in the usual order 
of reading a book, from left to right, and should carefully study 
