768 
moved the antennz, then the head, then 
the thorax, to and fro, and finally began to 
walk. 
Formica nitidiventris. 
(14) May 19, 4:08 p.m. Ant quiet, and 
confined in a test-tube as described in (18). 
Suspended the tube in the air near the ro- 
tating milled disk (12). At each sound 
from this apparatus the ant showed un- 
mistakable signs of agitation, quickly mov- 
ing the head and antenne. 
In addition to these, I may also mention 
an experiment tried on the colony as a 
whole with each of these species except 
Formica nitidiventris, with which I had no 
opportunity to try it. The colony being 
quiet in their nest under a plate of glass, I 
produced with the lips or with an instru- 
ment clear, shrill notes, taking the greatest 
care not to blow upon the nest or to allow 
anything else but the sound to disturb the 
colony. The ants instantly showed, by 
their quick movements in all directions, un- 
mistakable signs of excitement or alarm. 
I tried this over and over again with each 
of the three species, in the presence of vis- 
itors to the laboratory, and the result was 
invariably the same. All who saw it ad- 
mitted at once that their doubts as to the 
sense of hearing in those ants were entirely 
removed. 
As to the remainder of the experiments, 
lack of space prevents me from describing 
them, but let it suffice to say that by far 
the greater part of them gave results just 
such as those already described. 
The persistence of these affirmative re- 
sults led me to a conclusion which is em- 
bodied in the statement of the following 
thesis: The ants, or at least some of the ants, 
are capable of perceiving vibrations, conducted 
through the air or other media, which are audible ° 
as sound to the human ear. It willbe noticed 
that I do not assert that any of the ants 
hear, in the ordinary sense of the word ; 
neither do I deny it; my statement is 
SCIENCE. 
[N. S. Von. X. No. 256. 
merely that some of them are capable of 
percewing ordinary sound vibrations, which 
does not necessarily imply a true sense of 
hearing. However, in all the experiments, 
great care was taken in various ways to 
prevent the vibrations from reaching the 
ants through solids as media. And if it be 
true that this sensation, apparently due to 
a sense of hearing, is merely that of a me- 
chanical vibration or jarring produced by 
the sound waves (and hence would pertain 
in a measure to the sense of touch), how 
shall we explain the results of experiments 
like (3), (7), (9) and (11), which certainly 
indicate a sense of direction? And how 
shall we account for the fact, shown in 
many of my experiments, that some ants 
which pay little attention to being knocked 
and jarred about in their glass prisons are 
driven nearly frantic, apparently, by shrill 
sounds? The result of experiment (8) 
should also be noted as of special impor- 
tance. For this ant ( Cremastogaster lineolata) 
is a stridulating species, and the movement 
of the abdomen mentioned is one of stridu- 
lation, producing a minute sound; the sig- 
nificance of this fact is obvious, indicating 
aresponse on the part of the ant to the 
sound of the whistle. 
I might proceed to discuss at length the 
results of these experiments, arguing from 
standpoints based on the principles of psy- 
chology; but for the present it will be 
necessary, as before stated, to leave the 
experiments with their results as described 
to the consideration of the reader, and per- 
mit him to deduce his own conclusions. 
Le Roy D. WE Lp. 
IowA STATE UNIVERSITY. 
ARE THE TREES ADVANCING OR RETREAT- 
ING UPON THE NEBRASKA PLAINS?* 
Two years ago I presented a paper before 
this Section showing that there are reasons 
* Read before Section G, Botany, of the American 
Association for the Advancement of Science, August, 
1899. 
