1927] The Reaction of Datana Larvae to Sounds 131 
marked anatomical feature. The larvae of D. ministra feed on 
various species of Crataegus. They resemble the larvae of D. 
perspicua very closely; the most striking difference is due to the 
orange color of the prothoracic segment. The responses of the 
two species are similar, but those of D ministra are not as 
marked as those of D. perspicua. 
Preliminary tests demonstrated that these larvae give mark- 
ed responses to only two notes: middle C (512 vibrations) and 
F sharp above middle C (728 vibrations). The responses were 
very distinct. The instrument used in making the tests was a 
closed pipe with a movable plunger. Eleven larvae were used in 
each test. The number was purely arbitrary. They were taken 
from a large cage in which they were kept, and placed on a ver- 
tical stick. The tests were made after the caterpillars started to 
creep. In every case, efforts were made to protect the insects 
from air blasts from the pipe. 
In the critical series of tests, normal larvae of D. perspicua 
were used only as controls, but a complete set of tests was made 
with normal larvae of D. ministra. 
Attention was chiefly directed toward the role of the hairs 
in the detection of sounds. The methods employed were similar 
to those used by Minnich in 1925; the hairs were “loaded” with 
water or shellac. The liquids were sprayed on to the hairs with 
a nasal “atomizer.” As the water had a tendency to run off, it 
had to be frequently renewed. The shellac was the commercial 
orange product diluted with an equal volume of ethyl alcohol. 
Its value lay in its stability; the alcohol soon evaporated, leaving 
the droplets of shellac fixed on the hairs. These methods of 
treatment did not seriously injure nor inconvenience the larvae. 
Some specimens of D. perspicua were bathed with a 2 percent 
solution of procain. Although this inhibited responses, it was 
more or less injurious, and several of the insects so treated sub- 
sequently died. 
Ten trials were made with each group of larvae; five for each 
set of vibrations. Four specimens of D. perspicua were tested after 
removing the hairs from their bodies by clipping. Normal in- 
sects were also tested with a piano and a mandolin. The results 
of the experiments are tabulated as follows: 
