eet of cells of the two-layered body, they conduct impulses
from one part of the animal to another, and thus serve as coordinating
members of the community. For the first time, then, a nervous system as
such is set apart and specialized to devote itself to the two tasks of
sensation and coordination that are performed by nervous systems
throughout the entire range of organisms higher in the scale. But the
activities of _Hydra_, like those of _Amoeba_, are reflex and
mechanical,--that is to say, _given similar stimuli and similar
physiological states of the animal, the reactions will be the same_. A
little water-crustacean like _Daphnia_ may swim against the tentacles of
_Hydra_; it is stung to death by the minute cell-batteries which the
animal possesses, and then in a mechanical way the tentacles transport the
food to the mouth, through which it is passed inward to the digestive
cavity. There is nothing that can be called "mentality" throughout these
processes, but the series of activities is much more complex than in
_Amoeba_ because the whole organism is constructed more elaborately, and
because the special and peculiar mechanism directing the activities has
advanced to a far higher condition.

Passing to the jointed animals like worms and insects, we find nervous
mechanisms that are still more intricate, and with their advance in
structural respects there is a corresponding and correlated progress in
their functions. Because the whole organism has developed more highly
differentiated groups of organs to perform the several biological tasks,
such as eating and respiring and moving, it is necessary for the nervous
structures concerned with the direction of these actions to become more
efficient. An earthworm avoids the light of day and digs its burrow and
seeks its food by wonderfully cooerdinated activities of its muscles and
other parts, which are controlled by a double chain of ganglia along its
ventral side, connected with a similar pair of grouped nerve-cells above
the anterior part of the digestive tract. The ganglia of each segment
exercise immediate supervision over the structures of their respective
territory, while they pass on impulses to other ganglia so that movements
involving many segments can be properly adjusted. Everything an earthworm
does is controlled by the cells grouped in these ganglia, or scattered
along the intervening connecting cords. We speak of its acts as
instinctive, employing a term whi