AUDITORY AND SOUND-PRODUCING MECHANISMS. 603 
11. THE HALTERES OF THE BLOW-FLY. 
a. General Structure and Morphology (Plates XLII. and XLIII.). 
The halteres, which are commonly known in the Diptera 
as ‘ balancers,’ are rarely absent in the order. Weismann [2] 
showed that they are developed from the upper metathoracic 
imaginal discs, and they are now generally admitted to be 
homologous with the posterior wings of other insects. 
When it is said, however, that they are rudimentary wings, 
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