RHYTHMS IN BEHAVIOR 155 
starfish was prevented from using these rays and was al- 
lowed to turn only on those rays which it was least prone 
to employ. If, after a number of trials, the starfish came 
to employ the latter most frequently it would be fair to 
conclude that the animal had acquired a new habit of turn- 
ing. After one or two days’ training most of the individ- 
uals experimented on came to turn upon rays which they 
were at first disinclined to use. The effect of the training 
was not manifest, however, after twenty-four hours. In 
specimens “trained” for a week or more the habit formed 
persists, according to Jennings, for twenty-four hours or 
even several days. The data obtained on this subject 
were not extensive, and when we consider several sources 
of error involved, not entirely convincing; further work 
would be necessary before we could safely conclude that 
starfish form lasting habits. 
How shall habit formation in the starfish be interpreted? 
Moore has shown that irritation of an arm inhibits its ac- 
tivity and causes the starfish to use other arms in the right- 
ing movements; and the operation of handling the animal 
during its “lessons” so as to prevent a certain arm from 
being used might produce a similar effect. There is no evi- 
dence that there is any element of association involved, and 
it is not quite clear whether the basis of the habit lies in 
the nervous system or in other parts of the organization. 
RHYTHMS IN BEHAVIOR 
Georges Bohn has the merit of having discovered that 
the rhythms of activity which are produced in many animals 
by regularly recurring external conditions such as the alter- 
nation of day and night and the periods of low and high tide 
may persist for some time after the animals are withdrawn 
from the direct influence of the outer periodic changes. 
