GENERAL ARRANGEMENT OF ITS CONTENTS. 
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I. An Elementary or Introductory Series, by which the Introductory 
study of every group should commence, in which the leading ser?es. mentary 
features of the structure, and, as far as may be, the development 
of the various parts of some of its most typical members, are 
demonstrated in a clear and simple manner, and the terms used 
in describing and defining them explained by means of 
illustrative examples. This has been already carried out in 
the Department of Mineralogy, in a series of cases placed on 
the north or left-hand side of the gallery containing the rest of 
the collection. The introductory series to the zoological and 
botanical collections has just been referred to as under arrange- 
ment in the Central Hall. 
II. The Exhibited Systematic Series, in which the most Exhibited 
important types of animal, plant, or mineral forms are shown, series***" 
by means of carefully-selected and well-preserved specimens, 
arranged in a systematic manner, or one which exhibits, as far 
as may be, their natural relations to each other. Classification is 
an important feature in this series, which should be so complete 
and so arranged as to ensure that every visitor to the Museum 
can find, without recourse to assistance from the officials, every 
well-known and very distinct form of animal, plant or mineral, 
and satisfy himself about, at least, its external characters. In 
carrying out this ideal, great modifications must be made in 
practice, partly depending upon the readiness, or the reverse, 
with which the members of different groups lend themselves 
for exhibition, partly upon the exigencies of space, and partly 
upon special circumstances which render the exhibition of the 
leading forms of some groups of more interest than those of 
another. 
While the two series above mentioned have for their object 
the diffusion of scientific knowledge, the next ministers mainly 
to its advancement, and thus between them the twofold object of 
a National Museum of Natural History is carried out. 
III. The Eeserve or Study Systematic Series contains all Reserve or 
those exceedingly numerous specimens (in many groups, the gy*^ t - 
great bulk of the collection) showing the minute distinctions Series, 
which are required for working out the problems of variation 
according to age, sex, season and locality, for fixing the limits 
of geographical distribution, or determining the range in geo- 
c 2 
