structure and classification, the other with their living activities,
their habits, life histories, and reproduction. Both branches are usually
included under the terms Natural History, or Zoology, or Botany, and a
work on any group of animals usually attempts to describe their structure,
their classification, and their habits. But these two branches of
biological science are obviously distinct in their methods and aims, and
each has its own specialists. The pursuit, whose ultimate object is to
distinguish the various kinds of organisms and show their true and not
merely apparent relations to one another in structure and descent,
requires large collections of specimens for comparison and reference: it
can be carried on more successfully in the museum than among the animals
or plants in their natural surroundings. This study, which may be called
Taxonomics, deals, in fact, with organisms as dead specimens, and it
emphasises especially the distinguishing characters of the ultimate
subdivisions of the various tribes of animals and plants--namely, species
and varieties. The investigation, on the other hand, of the different
modes of life of animals or plants is based on a different mental
conception of them: it regards them primarily as living active organisms,
not as dead and preserved specimens, and it can only be carried on
successfully by observing them in their natural conditions, in the wide
spaces of nature, under the open sky.

The object of this kind of inquiry is to ascertain what are the uses of
organs or structures, what they are for, as we say in colloquial language,
to discover what are their functions and how these functions are useful or
necessary to the life of the animals or plants to which they belong. For
example, some Cuttle-fishes or Cephalopoda have eight arms or tentacles
and others ten. The taxonomist notices the fact and distinguishes the two
groups of Octopoda and Decapoda.