392 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
lunar-tidal rhythms do not depend upon any known kind of external 
cues for the measurement of the lunar-period lengths. 
The 24-hour rhythm seems very deeply ingrained in organisms. 
We showed a number of years ago that even if rhythms seemed com- 
pletely halted, as in the instance of color change in crabs held in very 
bright light for 10 or 12 days, a regular rhythm would reappear at 
once when the crabs were replaced in darkness. 
It has been satisfactorily demonstrated that an organism need never 
have experienced a single normal daily cycle in its life, and yet be 
capable of exhibiting a precise daily cycle. Hence the cycle cannot 
be contemplated in any sense as a period of day length remembered 
by the organism. It was shown long ago that beans grown in constant 
darkness show no rhythmic sleep movements, but a single brief light 
shock will start off a persisting 24-hour rhythm, the time of day of 
awakening onset, a function of time of the light shock. Fruit flies 
normally, as they are about to complete their development, emerge 
from their pupal cases as fully active flies about daybreak, Dr. Brett, 
in my laboratory, showed, however, that if a batch of eggs is laid and 
development is caused to occur wholly in darkness, flies emerge at all 
hours of the day. But if during the development of the fly larvae in 
darkness, a single flash of light, as brief as one minute, is given them, 
then the flies will emerge from their pupal cases, up to days later, after 
completing their development and pupating, at the same time of day as 
the time the light flash was given. The light flash could not have 
imparted information as to the length of a 24-hour period to render 
this possible. ‘The flies behaved quite as if they all had operating 24- 
hour rhythms of emergence but had had nothing by which to set them 
to the usual time of day. The brief light flash seemed to be treated 
by all the developing flies as the onset of a dawn, and with this, all 
the rhythms were synchronized. Flies normally emerge at dawn. 
A deep-seated daily rhythmicity of still unknown significance was 
discovered recently by Professor Binning and his associates. This isa 
rhythm of swelling of the nucleus of cells of a number of plants. In 
the daily changes the nucleus is largest about 6 in the morning and 
smallest at noon. I have spoken of this rhythm as deep seated because 
the cell with its contained nucleus constitutes the fundamental unit 
of organization of all living things, whether plant or animal. 
It is a commonly experienced phenomenon when we have made 
long east to west or west to east airplane trips that we have moved 
to a new longitude without having reset our own internal 24-hour 
rhythms. If, for example, we had lived for a time in New England 
and were accustomed to awakening at 7 in the morning, and now flew 
to take up residence in California, we would find ourselves, in Cali- 
fornia, awakening and disconcertingly being quite wide awake, about 
