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 antennae, 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 antennae shows little 

 specialization, is partly membranous, and in large part hidden by the globose 

 second antennal joints. Medianly, above the antennae, 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 antennse. 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 antennae and 

 above the clypeus usually shows no striictural 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 



