34 MOSQUITOES OF NORTH AMERICA 



confidently termed the second joint the " auditory capsule." His studies were 

 evidently influenced by his knowledge of the structure of the vertebrate ear, not 

 only in the interpretation of the anatomical structure of the organ, but, in con- 

 sequence, also of its functions. Probably inadequate microscopes and methods 

 contributed in large part to his errors. He described what he found as follows : 



" The auditory capsule is filled with a fluid of moderate consistency, opales- 

 cent, and containing minute spherical corpuscles, and which probably bears the 

 same relation to the nerve as does the lymph in the scalse of the cochlea of higher 

 animals. The nerve itself of the antenna proceeds from the first or cerebral 

 ganglion, advances towards the pedicle of the capsule in company with the large 

 trachea which sends its ramifications throughout the entire apparatus, and, 

 penetrating the pedicle its filaments divide into two portions. The central 

 threads continue forward into the antenna and are lost there; the peripheral 

 ones, on the contrary, radiate outwards in every direction, enter the capsule 

 space, and are lodged for more than half their length in sulci wrought in the 

 inner wall or cup of capsule. 



" In the female the disposition of the parts is observed to be nearly the same, 

 excepting that the capsule is smaller." 



Assuming the conditions to be such as described it was very natural to at- 

 tribute to the organ complex functions. Johnston sums up his reasons for be- 

 lieving the antenna an auditory organ of high perfection as follows : 



" The position of the capsules strikes us as extremely favourable for the per- 

 formance of the function which we assign to them ; besides which there present 

 themselves in the same light the anatomical arrangement of the capsules, the 

 disposition and lodgment of the nerves, the fitness of the expanded whorls for 

 receiving, and of the jointed antennae fixed by the immovable basal joint for 

 transmitting vibrations created by the sonorous modulations. The intra-cap- 

 sular fluid is impressed by the shock, the expanded nerve appreciates the effect 

 of the sound, and the animal may judge of the intensity, or distance, of the 

 source of the sound, by the quantity of the impression : of the pitch, or quality, 

 by the consonance of particular whorls of the stiff hairs, according to their 

 lengths ; and of the direction in Avhich the undulations travel, by the manner in 

 which they strike upon the antennce, or may be made to meet either antenna, in 

 consequence of an opposite movement of that part." 



A. M. Mayer, in the course of his researches in acoustics, made most interest- 

 ing experiments with the supposed auditory function of the antenna! hairs of 

 the male mosquito. With tuning-forks, he showed that some of the hairs are of 

 such a structure that they vibrate in response to sound-waves numbering 512 per 

 second. Other hairs vibrated to other notes, showing altogether a considerable 

 range. He says : 



" I infer from my experiments on about a dozen mosquitoes that their fibrils 

 are tuned to sounds extending through the middle and next higher octave of 

 the piano." 



Mayer carried his experiments farther, and, taking accurate measurements of 

 the thickness and length of two hairs which vibrated in response to the tuning- 

 forks Ut 3 and Ut 4, made large wooden models of them. The model of the 

 hair vibrating to the Ut 3 tuning-fork was a meter in length. These models 

 responded to vibrations of approximately the same nimiber as the hairs them- 

 eelves. 



