Nov., 1921 THE MIND OF THE FLOCK 185 
is by no means a phenomenon peculiar. to the Bush-tits, but one appearing in 
widely separated species of bird. 
Elsewhere in the animal kingdom we find parallel examples, suggesting 
that this type of behavior is still more generally distributed. Dr. E. C. Van 
Dyke informs me that the saw-fly larvae above referred to do not react sim- 
ultaneously as has been claimed (Newland, p. 38), but that the impulse can 
be observed to spread from individual to individual, probably as a tactile 
stimulus. Groos (1898, p. 208) remarks of gregarious mammals that ‘‘the 
playful act of one animal spreads through the whole company like a sudden 
econtagion’’, and observes, ‘‘when one cow in a herd leaps down the slopes 
where they are grazing, a large part of the herd will often follow’’. 
The behavior of crowds is essentially a phenomenon of the same sort. We 
do not see a thousand men become wildly enthused, or angry, or panic stricken 
in an instant. A few individuals are first moved by these emotions; by voice. 
or gesture, or appearance, their state of mind is conveyed to their immediate 
neighbors; the impulse spreads until the whole group is affected; their own 
shouts and cries excite them further, until we may witness a crowd of intelli- 
gent men shortly converted into an unthinking mob, with a unity of purpose 
which may lead to the most heroic or the most senseless acts. 
A ‘“‘Go West’’ movement or a Klondike stampede are phenomena essent- 
ially similar to the movement of a flock of Bush-tits from one chaparral clump 
to another. | 
An analogy may be drawn between spread of impulse in the group and 
the spread of an impulse through the nervous system of certain invertebrates. 
In a medusa, for example, or a sea-urchin, the part of the body immediately 
stimulated first responds; codrdination of action takes place slowly, spread- 
ing from part to part, until at last the whole organism is in motion. No part 
controls the rest. No reactions are controlled by the central nervous system. 
Von Uexkull (1909, p. 118) has called the sea-urchin a ‘‘republic of reflexes’’, 
and remarks ingeniously that ‘‘the legs (spines) move the animal’’, as con- 
trasted with the higher animals, where ‘‘the animal moves the legs’’. Which- 
ever part takes the lead depends upon circumstances, and the rest of the body 
gradually cooperates. 
Thus there is evident a comparison between codrdination of action in a 
simple animal and codrdination of action in the group. The flock behaves as 
a sort of primitive organism. 
Indeed it has been insisted by Huxley (1912, Chap. V) that any organized 
group may rightly be considered a form of individual. Whatever individuality 
the flock possesses, however, is usually of a very vague and imperfect type; 
the individualities of the component parts are incompletely merged with the 
individuality of the whole, and may even come into conflict with it or with 
one another, as when a band of Bush-tits undertakes to move in two or three 
directions at once (Miller, 1921, p. 126); ‘‘the legs move the animal’’; the 
individuals move the flock, rather than the flock the individuals. 
__In all the instances cited there is nothing which may not be explained 
with good reason on the basis of the spread of impulse through normal physi- 
cal channels. There may indeed be a hyper-sensitiveness to suggestion, a tend- 
ency for the individual to be alert and readily responsive to impulses coming 
pom his neighbors, but this, as Trotter (1916, p. 108) observes, is one of the 
‘undamental characteristics of gregarious animals. We have no occasion to 
