The difficulties that will be faced if common
fundamental features are not taken into account are as
follows
(i) The interrelationship among different animals cannot
be traced.
(ii) The picture of all animals at a glance cannot be
projected.
(iii) The development of other animal species cannot be
made.
(iv) There are numerous animal species which show great
variety of life. The various common fundamental
characters are taken into account for the classification
of these animals. If this has not been done, it is not
possible to deal with every living form separately at
individual level. Therefore, a classification has to be
based on the common fundamental characters for the
sake of study of diversity in living forms.