246 
Psyche 
[Vol. 94 
daily. There was clear ruby light during the dark hours, and contin- 
uously during constant darkness (DD). 
The group of ants of each species was placed in a two-chambered 
nest. Each chamber was a clear plastic box about 10 cm in diameter 
and depth. One chamber was darkened and had water and sugar 
water provided; the other served as an arena, dry and fully exposed 
to the light regime, and the counts were made there. To avoid inter- 
ference with the ant rhythms, food was renewed only when observa- 
tions were to be omitted for the following hours or days. 
Results 
Field 
Figure 1 shows the number of E. tuberculatum out, as assayed on 
the vine. A prominent increase occurred at dusk. The number was 
high during at least the first half of the night, and was low from 
dawn through the day. Fewer counts were made in the rest of the 
area around the nest entry (not shown), but they corroborated the 
high-night, low-day pattern. 
The pattern for E. ruidum , on the other hand, was diametrically 
opposite, high in the day and low at night, as based on two nearby 
nests of ruidum observed on the same days as tuberculatum (Fig. 1). 
Laboratory Light and Dark 
The number of E. tuberculatum out in the arena started rising 
from soon after light-off, to the highest peak early in the night (Fig. 
2). The number fell after the lights came on, remaining low through 
the light period, as in the field. The rise after light-off and the fall 
after light-on had also been seen in LD over a month earlier, good 
because so soon after collection from the field (but not shown here 
because so few night counts were made then). 
The E. ruidum counts were higher in the light period than at night 
(Fig. 2), and thus opposite to tuberculatum observed the same days. 
Constant Darkness 
What is the evidence for persistence of rhythm in the absence of 
the light-dark cycle? For each of the first 3 days of DD (Feb. 9-11), 
ant counts were made during what had been the light and the first of 
the dark part of the LD cycle. There was no obvious rhythm for E. 
ruidum , possibly because of so low a number of ants out in the 
