duced under the snow are arched inward toward 
the food hopper. The interpretation is as follows: 
When visual perception was possible the rats 
leaving hole 2 of the North Alley Burrow made a 
direct orientation toward the nearest point along 
the route to the food hopper regardless of whether 
this route might be taking them temporarily 
away from this primary goal. However, as soon 
as the visual perception of goals becomes impos- 
sible there arises a conflict between the orientation 
of movement of the animal toward intermediate 
and terminal goals. One might also interpret 
the origin of the snow tunnels here as resulting 
from a conflict between the directions of the routes 
of travel, rather than the locations of goals. 
L. Trail between hole 15, North Alley Burrow, 
and Passage 7. This trail most likely was initiated 
from North Alley Burrow hole 1 5. The remarkable 
approximation to the preexisting route on the 
ground is without clear explanation. According to 
the logic formulated for explaining routes A, G, and 
K. a rat heading out in the general direction of two 
spatially separated goals will actually move toward 
a point between these two goals. Presumably such 
orientation resulted from an averaging of the kin- 
esthetic orientation toward these separate goals. 
But in the present case the rat has three possible 
choices from North Alley Burrow hole 15: (a) to- 
ward the food hopper, (b) toward Passage 3 along 
route M, (c) along an underground tunnel toward 
North Alley Burrow hole 2. I can only hazard the 
speculation that the opposite attractions toward b 
and c essentially cancelled each other, and left the 
rat unhampered in its then major orientation to- 
ward the food hopper via the intermediate goal, 
Passage 7. 
M. Trail between hole 15, North Alley Burrow 
and Passage 3. Under the discussion of the pre- 
vious sections of subnivian trails I have indicated 
the direction in which I believe it most likely that 
the tunnel developed. However, in this case it is 
just as likely that a rat started from hole 15 and 
went toward Passage 3 as it was for the reverse 
direction of movement. With the exception of that 
portion of the trail nearest the North Alley Burrow 
there was an exact duplication of the preexisting 
trail. In the light of several of the previously dis- 
cussed segments of the subnivian trails it might be 
anticipated that regardless of whether the rat had 
started at hole 1 5 or at Passage 3 there would have 
been a deflection of the trail toward the Food Pen. 
Yet such was not the case. However, there was 
one set of conditions characteristic of the location of 
this trail that was absent to a marked extent for the 
other trails. This condition was that there were 
eight trees scattered along the route of this trail. 
In figure 65 is shown a series of diagrams of the 
relationship of these trees and other conditions to 
the location of trails at different periods over the 
history of the colony through this region. The 
route traveled by the rats on the night of January 
24-25 shows that they utilized these tree trunks as 
vertical cues for visual orientation. In observing 
the movement of rats along such trails it has been 
noted that the tendency to pause is greater at trees 
or other vertical objects. Although the rat may 
primarily utilize visual and tactile modes of per- 
ception in traveling to or by the next vertical ori- 
entation cue, the hypothesis is forwarded that at 
the same time the rat is becoming conditioned to a 
system of proprioceptive stimuli. Each time the 
rat alters its course by directing its movement to- 
ward another vertical cue, a different system of 
proprioceptive stimuli will be generated. When 
visual and tactile perception are impossible, each 
of the trees along the trail will act as an intermedi- 
ate goal, toward which the rat orients by kines- 
thetic sensation. On arriving at one tree the rat 
then responds by moving in the direction indicated 
by the system of proprioceptive stimuli associated 
with that place. In so long as the vertical cues to- 
ward which the rat orients are not too far apart the 
orientation will not be significantly affected by 
other more distant, but also more terminal, goals. 
N. Trail from limiting barrier fence to Passage 
3. Due to the fact that there was no wind very 
little snow had drifted back under the 18-inch 
overhang. Over most of the way the rats used 
visual perception since they started on the pre- 
existing trail and then gradually tramped down 
the deepening snow. This particular section gives 
no further information since the subnivian trail 
did not start until just before Passage 3. 
c. Summary of inferences concerning orientation during 
the formation of subnivian trails. 
1 . Visual and tactile perception were inoperative 
during the orientations leading to the formation 
of the tunnels. 
2. From the position in which a rat happens to 
be, more distant intermediate and terminal goals 
serve as points toward which the rat tends to 
direct its movement, even though it is unable to 
perceive the goal directly. 
78 
