DEVELOPMENT. 
225 
Function is the test of worth. Not mere work, how¬ 
ever; for we must consider its quality and scope. An 
animal may be said to be more perfect in proportion as 
its relations to the external world are more varied, pre¬ 
cise, and fitting. Complexity of organization, variety, 
and amount of power are secondary to the degree in 
which the whole organism is adapted to the circumstances 
which surround it, and to the work which it has to do. 
Ascent in the animal scale is not a passage from animals 
with simple organs to animals with complex organs, but 
from simple individuals with organs of complex function 
to complex individuals with organs of simple function: 
the addition as we ascend being not function, but parts 
to discharge those functions; and the advantage gained, 
not another thing done, but the same thing done better. 
Advance in rank is exhibited, not by the possession of 
more life (for some animalcules are ten times more lively 
than the busiest Man), but by the setting apart of more 
organs for special purposes. The higher the animal, the 
greater the number of parts combining to perform each 
function. The power is increased by this division of la¬ 
bor. The most important feature in this specialization is 
the tendency to concentrate the nervous energy towards 
the head (cephalizatiori). It increases as we pass from 
lower to higher animals. 
As a rule, fixed species are inferior to the free, water 
species to land species, fresh-water animals to marine, arc¬ 
tic forms to tropical, and the herbivorous to the carniv¬ 
orous. Precocity is a sign of inferiority: compare the 
chicks of the Hen and the Robin, a Colt with a Kitten, 
the comparatively well - developed Caterpillar with the 
footless grub of the Bee. Among Invertebrates, the male 
is frequently inferior, not only in size, but also in grade 
of organization. Animals having a wide range as to cli- 
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