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 of 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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