34 THE EARLY STAGES OF TABANID^ 



the walls of the capsule, the place of invagination seems to have 

 disappeared. 



Graber therefore decided that the organ must be a sense organ, 

 which, however, according to its peculiar structure and position can- 

 not be either an organ of touch, smell, taste, or sight, and is conse- 

 quently placed among the auditory organs. Graber also believed 

 that he found the two main features of a cystoid auditory organ, 

 namely a cyst-like cell system, connected with a nerve, and an in- 

 ternal fluid medium which may carry the sound. There were lacking 

 only the characteristic elastic appendages of the auditory cells. 



Graber assumes that under certain conditions the auditory cells 

 may be stimulated by waves of sound even in the absence of special 

 end organs, in the same way that the light-perceiving elements of the 

 eye in part are also affected by light-waves in the absence of special 

 terminal organs as found in highly developed organs of sight. 



The presence of the peculiar pedunculate bodies seems, more than 

 anything else, to have determined Graber' s view, in as far as they 

 form a good analogy to the otoliths commonly found in auditory or- 

 gans of the cyst-like type. The pedunculate bodies are comparatively 

 heavy, thick- walled bodies and are attached to the cysts by means of 

 thin and probably elastic filaments or strings ; they may be compared 

 with the clappers of a bell, which facilitate their function as otoliths. 



Graber classifies all auditory organs occurring among insects, as 

 (1) elementary organs, consisting of isolated hearing cells or auditory 

 hairs, (2) cystoid auditory organs, gymnotocysts, and chitinotocysts, 

 found in crustaceans and many insects, and (3) tympanal organs, pro- 

 vided with auditory rods as found in Orthoptera. The chordotonal 

 organs are related to the latter and differ by the absence of a tympanal 

 membrane. The organ in question is classified among the cystoid 

 organs. 



Henneguy found the same organs in small larvae resembling larvae 

 of Stratiomys (Lecaillon), (Plate 10, Fig. 109), which undoubtedly 

 belong to Tabanus. The organ in this instance (Plate 10, Fig. 110) 

 is different. It comprises a cellular mass situated in front of the 

 organ and evidently connected with the dorsal vessel, a capsule fol- 

 lowing it, containing two pigmented bodies arranged as described by 

 Graber, and, finally, a cyst prolonged backwards into a filament but 



