INTRODUCTION. 
To a large class of visitors, who desire to find in a zoologi¬ 
cal collection instruction as well as amusement, a brief state¬ 
ment of the meaning and the relative value of the groups into 
which the animal kingdom is divided by naturalists, will not 
be without interest. To arrive at a correct understanding of 
these, it is necessary to look at the animal world, not as a 
mere mass of living forms bearing haphazard resemblances to 
each other, but as composed of great family groups of beings, 
formed, more or less, on the same plan, varying, it is true, to 
a vast extent in its mode of expression, but all the forms of 
which, starting from a common point, may be arranged in 
more or less divergent series, presenting combinations of 
structural peculiarities, differing from each other to an extent 
somewhat proportionate to their distance from the starting 
point. 
The first complete systematic classification of living forms 
was made by the Swedish naturalist, Linnaeus, about the 
middle of the eighteenth century, chiefly from external resem¬ 
blances ; but the growth of the great conception of organic 
evolution within the past forty years has profoundly changed 
both the methods and the views of zoologists, and the systems 
now in use, based mainly upon anatomical characters, aim at 
indicating the real relationship and successions in time, borne 
to each other by species now existing and those already ex¬ 
tinct. 
( 3 ) 
