36 MOSQUITOES OF NORTH AMERICA 
very rudimentary way, auditory in function. Child already observed the great 
sensitiveness of the swarms of dancing males to sound vibrations, 
“ moreover not alone to the higher, but also to deeper tones. If one sings a deep 
note in the vicinity of a swarm, the entire swarm is immediately thrown into 
confusion which lasts several seconds. . . . Faint noises have the same effect, 
naturally in a lesser degree. I have observed the same from the whistle of a loco- 
motive, even when this was one or two kilometers away. If one approaches a 
swarm of gnats in a boat, upon some sudden noise, such as a stroke of the oars, 
the entire swarm is thrown into a wild dance and frequently flies away or dis- 
solves. As, however, with great care, even with fairly rapid movements, one can 
get close to the swarm without the gnats reacting in any way, it follows that the 
disturbance is caused by the sound and not by a visual impression. From these 
observations of course nothing can be concluded regarding the location of the 
organs of hearing; it is only proved thereby that the gnats are very sensitive to 
sound. But because it is in these insects that an organ occurs which appears 
especially equipped for the reception of air-vibrations, the probability of a con- 
nection with that behavior is very great.” 
While it is evident from the foregoing that mosquitoes react to sound-waves, 
it is by no means clear that they can perceive them as such. If the sound-im- 
pressions are received through the antenne, as the organization of these ap- 
pendages seems to indicate, it is still to be doubted that there is a differentiation 
of the impressions produced by sound-waves and other stimuli, such as a current 
of air, or between sounds of different pitch. Child’s conclusion was that the 
function of Johnston’s organ was originally the perception of tactile stimuli, 
and that when it became more highly developed it also served for the perception 
of sound-waves. “The resulting ‘auditory impression’ is a modified tactile 
impression.” It is worthy of note, in this connection, that the male mosquitoes 
emit a very high-keyed song while swarming ; in fact, this sound is so high that 
it is probably beyond the range of many human ears. 
The part of the head inclosed by the eyes and bearing the antenne shows little 
specialization, is partly membranous, and in large part hidden by the globose 
second antennal joints. Medianly, above the antenna, and resting against the 
front margin of the eyes, is a small chitinous piece. In the Culicini this is 
usually rather poorly defined, subquadrate or more or less triangular, with its 
base resting against the margin of the eyes and the apex projecting forward be- 
tween the antennz. In the Sabethini it is conspicuous, although small, in those 
forms in which the eyes are separated above by a narrow wedge. This wedge, in 
fact, is a backward extension of the chitinous piece in question ; the portion pro- 
jecting forward beyond the margin of the eyes is prominent and may be either 
pointed or truncate in front. That part of the front below the antenne and 
above the clypeus usually shows no structural peculiarities. In one sabethid 
genus, Rhunchomyia, however, this portion is produced into a tubercle which 
projects just above the clypeus. 
CLYPEUS. 
The clypeus is large and prominent, chitinous, and projects above the inser- 
tion of the proboscis. Its development is unusual, and this is to furnish a place 
of attachment, on its inner walls, for the powerful muscles of the epipharynx. 
It is strongly chitinized above and its shape is roughly globose, or roundedly 
