1917] EsterJij: Occurrence of Rhythms in Geotrupisni 395 



It is shown in the table tliat a jjood many more animals are found 

 in the upper than in the lower two-fifths if the tubes are kept in tlie 

 light. Temperature seems to have no effect on the distribution, since 

 experiments were made at intervals from July through December, 

 during which time there has been a reduction in average room 

 temperature of 8° C. 



The second line of table 1 contains a summary of all the records 

 of distribution in darkness without regard to an.y modifying factor, 

 and it is shown that the number of animals decreases in the upper 

 and increases in the lower sections in comparison with the proportions 

 in the light; the center of distribution is also at a lower level in the 

 dark. This general result as regards darkness is affected, however, 

 by two conditions — temperature and time of day. The effects of these 

 factors can be seen in such a tabular summary as that in table 2, 

 wherein the records in the second line of table 1 are arranged accord- 

 ing to the time of day at which the observations were made, as well 

 as according to temperature. It should not be forgotten that the 

 experiments were set up during the forenoon and the animals kept in 

 the dark except for the brief time necessary to note their distribution. 



TABLE 2 



ACARTIA TONSA, AdULTS OF BOTH SeXES : SUMMART OF EeCORDS OF DISTRIBUTION 

 IN A COLnMN OF WATER IN DARKNESS, TO ShOW EFFECT OF 



Temperature and Time of Day 



Note. — The reason for the proportional reduction in numbers from late after- 

 noon on, as compared with the rest of the day, is that some individuals die in the 

 course of the day, so that as the tube is left standing tlie wliole numljer becomes 

 less. This, however, does not affect the percentages. 



It is obvious that at the higher temperatures there is a marked 

 upward movement of the animals from 6 to & p.m. This is shown by 



