42 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of sixty genera belonging to all the orders. These tables sbow fur- 

 ther that their most usual seat is the hind-wings or halteres, the next 

 the fore-wings ; the legs are more often thus employed in the lower 

 orders (Hemiptera, Neuroptera, and Orthoptera) than the wings. 



As regards their phylogeny, Prof. Graber considers the serially 

 arranged organs to have been derived from an original dispersed 

 condition, and the simplest scolopoferous forms from nerve-endings 

 devoid of rods. 



The physiological division of Prof. Graber's work* leads up to 

 the conclusion that the function of these organs is probably auditory. 

 Sounding a loud note on a violin not far from a specimen of Blalta 

 germanica engaged in walking across the floor, is followed by the 

 immediate cessation of the movement ; this may be repeated several 

 times with a like result if the intervals between the notes are not too 

 short. With specimens placed in a wide glass vessel the same thing 

 occurs ; a Blatta deprived of its eyes, and suspended by one leg and 

 allowed to become quite motionless, manifested great excitement, 

 jerking itself upwards, on a loud note being sounded on a violin at 

 about a metre's distance. Coccinella behaves similarly, but in a less 

 striking manner. Of water- insects, Graber finds that Gorixa darts 

 wildly about when the edge of the glass side of the aquarium is tapped 

 with a glass rod; further experiments show that mere mechanical 

 vibration is not the cause of the movement, but that it is due to 

 pure sound. Important evidence was obtained as to the quality of 

 sound audible to these insects ; for neither did a loud but deep toned 

 hand-bell sounded outside the aquarium, nor the lower notes of a 

 violin, produce much result, but the notes E to D, &c., on the latter 

 instrument always increased in the most striking manner the number 

 of water-bugs aroused. The water-beetle LaccopMlus is most readily 

 excited, and in great numbers ; Bytiscus marginalis and Nepa cinerea 

 also reacts strongly to loud sounds. On the other hand many aquatic 

 larvae, especially Ephemeridce, exhibit no distinct perception of sound, 

 though remarkably sensitive to mechanical agitation of the surround- 

 ing medium. Variations in the intensity of sound may be demon- 

 strated to be perceptible to insects.. 



Facts such as the great manifest sensitiveness of many insects to 

 the grasshopper's chirp, too great to be explained as due to tactile 

 sensation, militate against the hypothesis that the sense involved 

 is merely tactile. Comparison of the structure of the tympanal 

 chordotonal organs with that of the vertebrate ear leaves it probable 

 that the former have acoustic properties ; in the Gryllidse the tym- 

 panum and auditory meatus are both represented (the latter by 

 tracheal tubes, the former by a peculiar enlargement of the trachea), 

 the organ of Corti is of course represented by the scolopoferous and 

 other chordotonal nerve-endings already described ; they exhibit a con- 

 siderable variety in the amount of their sympathy with the movements 

 of the tympanic organs in the different cases. 



The primitive forms of chordotonal organ appear to have the 



* Loc. cit., xxi. (1882) pp. 65-145. 



