36 
CURT P. RICHTER 
on the foreshore of the sandy beaches of Normandy and 
Brittany. These workers found that the habits of this animal 
are to a very considerable extent dependent on the movements 
of the tide. Just before the tide reaches them at each flow 
they disappear into the sand, and just as soon as they are 
uncovered during the ebb they come up on the surface again. 
In this a very regular alternation of downward and upward 
movement is set up. Bohn (3) and Keeble (4) found further 
that when these animals are scooped up in a cup with some 
sand and placed in the laboratory where they are no longer 
subjected to the periodic coming and going of the tides they 
still continue for several days to make the upward and down¬ 
ward movements just the same. Benjamin Moore (5) has also 
described the persistence of a rhythm in absence of the wonted 
stimulus in the case of phosphorescent organisms in the sea. 
The organisms give off their light only at night. When they are 
placed in a dark room this daily alternation of phosphorescence 
and inactivity persists over a period of fourteen days after which 
time the animals usually die. 
VII. ON THE ORIGIN OF SPONTANEOUS ACTIVITY 
Throughout all of the experiments described thus far in this 
present study it was seen that a large part of the activity of the 
rat cannot be accounted for in terms of stimulation from outside 
sources. It was shown how some of the ever present factors, 
such as illumination and temperature may modify the expression 
of activity, but it was also shown that these factors could not be 
called upon to account for the activity. For this reason all that 
part of the activity of the rat that occurs in situations free from 
all external stimuli was spoken of as “ spontaneous ” activity. 
The source of this activity must lie somewhere within the organ¬ 
ism. What organ or mechanism is there within the body of the 
rat which might serve to bring about this gross bodily activity? .< 
In looking for this source of stimulation the chief characteristics 
of the manifestation of spontaneous activity studied above must 
be kept in mind; this is the very regular alternation of periods of 
activity and inactivity at the rate of ten to fourteen per twenty- 
