Marcu II, 1915] 
NATURE 39 

not visited for a fortnight, they will return home, 
quickly, confidently, and by the shortest w ay. 
These are four illustrative facts out of many, 
and the question is how they are to be interpreted. 
Some authorities still believe that there is no 
getting past the assumption of a non-analysable 
sense of direction, such as the Martian of Du 
Maurier’s novel had of the North Pole. Others 
have swung to the opposite extreme of taking too 
simple a view, and maintain that it is altogether 
a question of scent: ants, like dogs, living in a 
smell-world. Others again lay too heavy a burden 
on muscle-memory, and others on visual impres- 
sions gathered by the way. Dr. Brun shows 
clearly, we think, that the power of way-finding 
is usually a composite product, and that there is 
no mysterious sense of direction. 
Of course, there are ants and ants, and there is 
no doubt that the scent of the nest, of the food, 
and of the pupe sometimes counts for much. If 
two adjacent sections of a pre-arranged ant-road 
be lifted and interchanged, the travellers go on 
just as they were doing; but if a section of the 
road—-say a zinc plate—hbe lifted and _ replaced 
with its ends reversed, the ants seem to be per- 
plexed at the boundaries, and there may be a 
temporary block. [acts of this sort have given 
rise to over-ingenious theories of polarised scent, 
of positive and negative scent, and so forth. This 
much seems clear, that. the nest-smell gets fainter 
in proportion to the distance from home, and that 
the food-smell increases as the source of supply 
is approached; and it is very instructive to find 
that if an ant of one of the olfactory species be 
transported and placed in the middle of one of 
the ant-roads, it does not go home right away, 
but takes a tentative run first in the one direction 
and then in the other. .In some genera, however, 
such as Formica, smell counts for little, and the 
obliteration of the scent by brushing the road or 
pegging down a spread-out newspaper does not 
disturb the homing. In connection with smell, it 
may be noted that the seat of the olfactory sense 
is in the tips of the mobile antenna, where tactility 
is also located, so that tactile and olfactory im- 
pressions are closely combined. 
To many ants the illumination is much more 
important than scent, as Lord Avebury proved 
long ago. He got his ants to make a path across 
a wooden disc, concentric segments of which could 
be rotated, and found that if he turned a ring so 
that an ant on its journey was made to face the 
wrong way, it righted itself and proceeded in the 
old direction. But this was not the case when 
he made the experiment in uniform shade, or when 
he shifted the light at the same time as he rotated 
a segment of disc. One of Brun’s experiments 
with a species of Lasius is very instructive. It 
was marching with the sun directly in its eyes, 
when the experimenter put an extinguisher over 
it, and kept it prisoner from 3 to 5 p.m. When 
it was set free at five o'clock, it turned its back 
on the postion which the sun had reached, moving 
through 30°, and set off in a straight line home- 
wards, eventually turning sharply to the left to 
NO. 2367, VOL. 95] 

reach its original starting-point. Numerous ex- 
periments confirm the view that the direction of 
the light serves as a compass. When Santschi 
shut off the sun with a large shade and made a 
false sun by means of a mirror, he got the ants, 
even on one of their main roads, to march in a 
direction either at right angles to the original one, 
or Opposite to it, according to the position of the 
mirror. If, in the absence of sunlight, there be 
equal bipolar illumination of a given area, there 
is In many species no orientation. 
From waxing and waning scent and from 
differential illumination, ants seem to build up 
associations, but this is not all. There is evidence 
in some cases of a memory of muscular move- 
ments, especially of the distance traversed, as if 
the ant kept its eye on a pedometer. There is 
something” very interesting, too, in the pheno- 
menon technically known as Turner’s curves. A 
solitary ant that has travelled successfully from a 
considerable distance reaches a point quite near 
the nest; but instead of going on confidently, it 
stops.as if perplexed. In many instances—S8o per 
cent. in Cataglyphis bicolor—it proceeds to de- 
scribe concentric curves, it’ may be for 5-15 
minutes, and gradually draws near to the door 
of its home. Is it seeking for a sign, which might 
be a shining stone among the sand, or a scent, 
or the faint stridulation of one of*its kin? Is it 
method, very willing 
combination of 
a trial and error 
any hint or 
pursuing 
to be helpéd by 
hints ? 
In some -cases, 
proved a bareesthesia, 
Formica rufa,’ Brun has 
or feeling of gravity. A 
table was gently tilted, with the nest at the foot of 
the. slope; a feast of -honey was placed in. the 
centre; the ants climbed straight up and straight 
down again. But if, while an ant was supping 
honey, the table was gently tilted in the opposite 
direction, so that the way to the nest was up-hill, 
the ant persisted in going down-hill as before— 
away from, not towards, home. Among the 
highest ants Brun finds distinct evidence of definite 
local memory, based on visual, topographical, and 
topochemical data, and lasting for two or three 
weeks at least. And only thus can we understand 
the confidence with which one of these creatures, 
transported to a distant part of its range, will 
make for home. There are ants which trust mostly 
to scent, and others which are largely guided by 
the direction of light, but for the higher ants the 
orientation is a complicated process, the outcome 
of the registration of manifold imprints received 
from the outer world—imprints relating to the 
quantity and quality of scents, the general direc- 
tion of light, the illumination of particular objects, 
the slope of the ground, the feel of things, the 
distance travelled, the turns of the road, ihe direc- 
tion of the wind, and even, perhaps, sounds. 
Individual ants hereditarily endowed with great 
sensitiveness, hereditarily attuned to receive cer- 
tain kinds of tidings, serve an apprenticeship in 
the establishment of associations and reach a 
degree of perfection probably unsurpassed. Such 
is Dr. Brun’s general position, which he defends 
0 
e.g., 
