2o6 
PHYSIOLOGY: H. SHAPLEY 
Proc. N. a. S. 
taining the density of a file, for the estabhshment of new trails over some 
special terrain, or for other experiments. 
The large population of the nests makes possible the establishment of 
files of sufficient density for statistical treatment of the observations of 
speed. The population of colonies of Liometopum and of Iridomyrmex 
humilis is to be numbered by the tens of thousands. On an average patrol 
during the warmer months, 100 ants pass a given point in one minute 
(see table III, p. 209). From one nest on Mount Wilson, in the summer of 
1919, four files issued, and every day, under favorable conditions of weather, 
70,000 ants went out along each file and nearly 70,000 ants came in. 
The observations tabulated below were made on Mount Wilson (alti- 
tude 5700 feet) on ants from a nest of L. apiculatum, located in the basal, 
slightly-decayed trunks of a group of Quercus ckrysolepis Liebm. This 
species of Liometopum is not assigned to the state in Wheeler's "Mountain 
Ants of Western North America."^ The subspecies luctuosum Wheeler, 
however, has been taken on nearby mountains* and probably occurs on 
Mount Wilson. In a discussion of California ants, Woodworth^ states 
that "Liometopum is a very rare insect," it is probably uncommon, there- 
fore, in many parts of the state, but in the San Gabriel mountains it is by 
far the most numerous ant, with the species occidentale Emery predominat- 
ing.' 
Of the nine different "speed traps" set up for the study of the nest of 
L. apiculatum, Stations A and Y were principally used. The former is 
at the base of a concrete wall some 50 feet from the nest; the latter, on 
another trail, is on a plank surface about 2 feet from the main nest 
openings. These two pieces of trail are of comparable smoothness, and 
each is 30 centimeters in length. The time required for individuals to 
pass through the speed traps was recorded (with a stop watch for high 
temperatures), together with an indication of the size of ant and its direc- 
tion of travel. At the beginning and end of each observation, which is 
the mean time in seconds for about 20 individuals, the temperature was 
read from a thermometer, the bulb of which was placed against the wall 
or board, some 10 or 15 millimeters from the trail. 
As the observations are made within a few yards of a special station 
maintained by Mr. Hoge for the United States Weather Bureau, we have 
available, for all the observations on speed, continuous graphical records 
of the precipitation, wind- velocity, temperature, and barometric pressure, 
as well as semi-daily cloud and psychrometric observations. 
It was found from the first observations that the kinetic response for 
these ants is essentially a function of temperature alone — other meteoro- 
logical conditions (except rain, of course) having very little if any direct 
effect on speed. Even the influence of light and time of day are extremely 
small compared with the influence of temperature. If the speed is de- 
