1929] 
Myrmecocoles of Formica ulkei 
209 
out the Chicago area from April to October on the forest 
floor under leaves, and under bark of logs by day. It is 
evident, then, that a photo-negative, predaceous carabid 
should be at home in the dark, moist galleries of ulkei. 
The degree of positive or negative response to light was 
calculated in percentage of time the animal spent in the 
illuminated or darkened portion of the petri dish. Under 
these conditions, incurva was consistently 85 to 90% photo- 
negative. 
2. The pselaphids, Batrisodes, were less strongly photo- 
negative averaging 60% of the time in the darkened area. 
3. The blind Leptinus testaceus was completely indif- 
ferent to the light used, walking about the periphery of the 
petri dish in a steady movement, half of the time in the 
shadow, and half of the time in the light, which is in 
accord with its morphological make-up. 
It is clear that light does not play the prominent role that 
moisture does in these last two species of myrmecocoles. 
Activity 
The carabid, Tachyura incurva, the pselaphids, Batrisodes 
globosus and denticollis, and the leptinid, Leptinus testa- 
ceus, are as distinct in their locomotion and general activity 
as they are in morphological habitus. The pselaphids have 
a rather slow, regular walk, their legs moving in a stiff 
clock-like precision reminiscent of many Histeridae and the 
parnoid families, Dryopidae and Elmidae. They are es- 
sentially awkward, readily become upset and right them- 
selves with the greatest difficulty. 
On the other hand, Tachyura is much more active, and 
rights itself more easily. Leptinus testaceus, in consequence 
of its great width in proportion to its depth of body, loses 
its balance only rarely and then rights itself with ease. 
Being so flat it may creep into narrow crevices between 
particles of soil and hide, as was frequently observed, the 
general body plan reminding one of the flattened Cucujidae, 
Nitidulidae, the histerids Hololepta and Platysoma, the flat 
bark bugs, Aradidae, the exotic forms, as the carabid, 
