Vol. 6, 1920 
PHYSIOLOGY: H. SHAPLEY 
205 
measured under different conditions of light, air-temperature, relative 
humidity, wind- velocity, and barometric pressure, and at different times 
of the day and during all seasons of the year. The trails are maintained 
for long intervals of time, many of those of Liometopum apiculatum and 
L. occidentale on Mount Wilson have not changed during two years of 
observation. Colonies of the closely related L. microcephalum of Europe 
are also known to maintain constant trails for several years. ^ Ants 
running in these files, whether toward or away from the nest, are for the 
most part unburdened, their function apparently being mainly that of 
patrol. 
Another characteristic of the Liometopa, which is very fortunate for this 
research, is that they are equally diurnal and nocturnal in habit — a char- 
acteristic that permits continuous series of observations as well as favorable 
^opportunities for the investigation of natural phototactic reactions. 
The conspicuous differences in stature of the workers of Liometopum 
allow the possible correlation of activity and hardihood with size. The 
average live weight of a worker maxima of L. apiculatum is, according 
to my measures, about five hundredths of a grain (140,000 to a pound) ; 
the average worker minor weighs half as much, but the extremes of weight 
for maxima and minima are probably in the ratio of four to one. 
The wide range of temperature, humidity, wind, and light, throughout 
which these ants are active, enables a thorough testing of the extent to 
which the various meteorological factors are involved in kinetic reactions. 
The files are maintained with the relative humidity near its maximum of 
100%, or when as low as 5%; the patrols are running when the tempera- 
ture is 38° centigrade (over 100° F'ahrenheit) and also when it is less than 
8°. After a few warm day3 late in December thousands of ants of two 
species of Liometopum, on Mount Wilson, were out of their nests only a 
few feet from banks of snow. 
There is a distinct advantage for thermokinetic studies in the compara- 
tive freedom of the patrolling Liometopa from the erratic motions which are 
characteristic of many kinds of insects, or which are in fact characteristic 
of most active animals of all the higher phyla. It is this common irregu- 
larity and discontinuity of action that usually prevents quantitative 
measurement of the kinetic responses of cold-blooded animals. A fixed 
patrol of Dolichoderines from a populous colony, however, is essentially 
a steady flow of animal energy ; its quantity is governed largely by food and 
its speed by meteorological conditions. Except at low temperatures the 
normal speed of running appears to be very near the maximum speed 
possible under the prevailing conditions. For temperatures below 15° 
centigrade the excitation of battle or food temporarily increases activity. 
The California Liometopa are carnivorous, granivorous, and aphidicolous. 
This catholicity of taste permits successful baiting for the purpose of main- 
