546 The American Naturalist. [July, 
ments wherever we find them. Even if Mr. Spencer’s un- 
differentiated protoplasmic movements had existed, natural 
selection would very soon have put an end to it. There 
is a characteristic antithesis in vital movements always. 
Healthy, overflowing, outreaching, expansive, vital effects are 
associated with pleasure; and the contrary, the withdrawing, 
depressive, contractive, decreasing, vital effects are associated 
with pain. This is exactly the state of things which the 
theory of selection of movements from overproduced move- 
ments requires, i. e., that increased vitality, represented by 
pleasure, should give the excess movements, from which new 
adaptations are selected; and that decreased vitality repre- 
sented by pain should do the reverse, i. e., draw off energy and 
suppress movement.’ 
“Tf, therefore, we say that here is a type of reaction which 
all vitality shows, we may give it a general descriptive name, 
i. e., the “ Circular Reaction,” in that its significance for evolu- 
tion is that it is not a random response in movement to all. 
stimulations alike, but that it distinguishes in its very form 
and amount between stimulations which are vitally good and 
those which are vitally bad, tending to retain the good stim- 
ulations and to draw away from and so suppress the bad. The 
term ‘circular’ is used to emphasize the way such a reaction 
tends to keep itself going, over and over, by reproducing the 
conditions of its own stimulation. It represents habit, since 
T It is probable that the origin of this antithesis is to be found in the waxing 
and waning of the nutritive processes. ‘‘ We find that if by an organism we 
mean a thing merely of contractility or irritability, whose round of movements 
is kept up by some kind of nutritive process supplied by the environment— 
absorption, chemical action of atmospheric oxygen, etc.—and whose existence is 
threatened by dangers of contact and what not, the first thing to do is to 
a regular supply to the nutritive processes, and to avoid these contacts. But the 
organism can do nothing but move, as a whole or in some of its parts. So then 
if one of such creatures is to be fitter than another to survive, it must be the 
creature which by its movements secures more nutritive processes and avoids 
more dangerous contacts. But movements toward the source of stimulation keep 
hold on the stimulation, and movements away from contacts break the contacts, 
that is all. Nature selects these organisms ; fread — she do otherwise?..- - 
We only have to suppose, then, that the by natural 
selection drained off in organic expansions, to get the division in movements 
which represents this earliest bifurcate adaptation.” (Ref. z p- 
