1884.] Growth, its Conditions and Variations. 1093 
chased deer and antelopes are kept in frequent swift motion. In 
fact the smallest Herbivora are those that trust to flight for safety, 
the medium sized those that need rapid motion in food getting 
but are safe from the attacks of Carnivora, or able to defend 
themselves, while the largest are those which need rapid motion 
neither for flight nor food getting. The desert-living camel, for 
instance, must be able to move very rapidly from oasis to oasis. 
And the horse needs swift motion over the partly barren plains 
which form its native home. But neither of these has occasion 
to fly from enemies. 
Nervous activity is also repressive of growth, and the larger 
animals of each tribe are usually the duller mentally. But this 
is not the case where mental shrewdness replaces activity in the 
obtaining of food, or where the more intellectual animals possess 
highly efficient food-taking organs. The cuttle-fish is the largest 
and probably the most intelligent of mollusks, but its remarkably 
powerful weapons of assault enable it to obtain much food with 
little exertion. The same is the case with the elephant, whose 
trunk gives it special advantages in food getting. In these cases 
such mental energy as is exercised is correlated with physical 
sluggishness. In another case, that of the ants, the mental and 
Physical energies are both in high activity, and this is perhaps a 
main reason why the ants, with plentiful food and no reproduc- 
tive exhaustion, remain such small members of the insect race. 
But a still more important agency in the growth of animals is 
the efficiency of their weapons of assault and their powers of 
motion in obtaining them a plentiful supply of food. In all cases 
the larger animals are those best adapted and situated for obtain- 
ing food with the least exercise of muscular and nervous func- 
tions. In this latter particular the sedentary animals are at an 
advantage, but it is far more than counterbalanced by the ineffi- 
ciency of their means of capture. Unable to go in search of 
food, they are restricted to such food as they can bring to them 
by making currents in the water, or which they can capture in 
Passing. To the former purpose the cilia of Protozoa, sponges, 
the lower mollusks, &c., the winnowing arms of barnacles, &c., 
are applied; to the latter the. tentacles and t 
Ceelenterata. Parasitic animals are also included in this category. 
None of these animals can grow to a great size, since the quan- 
tity of food they can obtain is necessarily very limit 
