THE HALTERES OF THE BLOW-FLY. 615 



having a purely mechanical function, producing currents of 

 air, or limiting the excursions of the wing ; (4) organs of 

 hearing; and (5) organs of equilibration, balancers. 



Historical and Critical. Gleichen [3] , in 1764, thought them 

 to be analogous to drumsticks, which produce the hum of the 

 insect by striking the great wing scales ; and Landois [281] 

 held that their vibrations set in motion a portion of the 

 spiracular valve, which he termed the ' Brum-ring.' Neither 

 of these views are tenable, and have received little, if any, 

 support. 



Braxton Hicks, in 1856-57, thought their function olfactory ; 

 and Loew [293], discarding Hicks's view, suggested that they 

 assist in respiration, by producing currents of air in the vicinity 

 of the metathoracic spiracle. These views are not only un- 

 supported by evidence, but are quite inconsistent with the 

 results of direct experiments ; and it may be remarked, in 

 relation to Loew's theory, that the result of their vibration 

 would be immaterial as compared with the currents of air pro- 

 duced by the movements of the wings ; further, if I am right 

 in my contention that carbon dioxide is not excreted from the 

 spiracles, such currents are unnecessary for the respiration of 

 the insect. 



Jousset de Bellesme, in entire ignorance of the complexity and 

 minute structure of the halteres, supposes that they act as 

 stops to the wings ; he regards them as stiff pegs which check 

 the backward and downward movement of the wing by acting 

 on what he terms the axillary areolus. His brochure is a 

 record of some apparently carefully carried out experiments, 

 one of which, if it can be credited, is of the highest interest, as 

 he states that insects deprived of the balancers have the power 

 of flight restored if a tail of horse-hair several centimetres long 

 is glued on to the extremity of the abdomen. Whether this 

 observation is correct or not, the conclusions of Jousset do not 

 appear to me to be justified by his facts, and a theory which 

 entirely ignores the great complexity of the halteres and their 

 gigantic sensory nerves, great ganglia and sensory nerve endings, 

 cannot be accepted as satisfactory. 



