HALTERES 25 



the alula, antisquama, and squama. The ,s(|iiaiiia i.s thickei- tliaii 

 the rest, and is attached posteriorly to the wino-i-oot between the 

 mesoscutuni and the lateral plates of the postscutelluni. It covers 

 the haltere, as in all " calyptrate " Muscidae^. 



The Halteres. The halteres or balancers (fig. 6 hal.) are gene- 

 rally considered to represent the rudimentary metathoracic wings. 

 They are covered by the squamae, and are situated on the sides of 

 the thorax above the posterior spiracles. Each consists of a conical 

 base on which are a number of chordonotal sense-organs and on 

 this base is mounted a slender rod, at the end of which a small 

 spherical knob is attached. The wall of the distal half of this 

 sphere is thinner than the proximal half, and in preserved speci- 

 mens is generally indented. Experiments show that the halteres 

 are organs of a static function. They are not balancing oi'gans in 

 the sense that they are equivalent to the balancing pole of a rope- 

 Avalker. They also have probably an auditory function. They are 

 innervated by the largest pair of nerves in the thorax. 



^ The nomenclature of Comstoek and Needbam has not yet been adopted by 

 dipterologists in general, but on account of its morphological value, it may in 

 course of time replace the present confused system. It may, therefore, be useful if 

 the nomenclature employed in the foregoing description be compared with those 

 most usually employed. 



Longitudinal Nervuees. Ci. Costal. .SV-j . Mediastinal; auxiliary. Ej . Sub- 

 costal; 1st longitudinal, ii. 2 + 3. Radial ; 2nd longitudinal. /^. 4 + 5. Cubital ; 3rd 

 longitudinal; ulnar (Lowne). J/. 1+2. Median; 4th longitudinal; discal (Verrall). 

 il/. 3 + C(/i. Submedian; -^th longitudinal; postical (Yerrall). .^i. Anal; 6th longi- 

 tudinal. Pseudonervure ; axillary; 7th longitudinal. 



Transvekse Neevures. h. Humeral; 1st transverse ; basal cross-vein (Verrall). 

 rm. Discal; 2nd transverse; middle cross-vein (Verrall); medial transverse; anterior 

 transverse (Austen), m.cu. Anterior basal transverse (Austen); lower cross-vein 

 (Verrall); postical transverse (Lowne). m. Posterior transverse (Austen); postical 

 cross-vein (Verrall); discal transverse (Lowne). cxi.a. Posterior basal transverse 

 (Austen); anal cross-vein (VeiTall) ; anal transverse (Lowne). 



Cells. C. Costal. 1 C. Second costal. Sc. Third costal (Lowne correctly calls 

 this " sub-costal"). 1 i?. Marginal. 3 -R. Sub-marginal; cubital (Lowne). 5 -R. First 

 posterior cell (Austen); sub-apical (Lowne and Verrall). 2il/2. Second posterior 

 cell (Austen) ; apical. 1 Cu. Third posterior cell (Austen and Verrall) ; patagial 

 (Lowne). 2il/i. Discal (this term is used also in Lepidoptera, Trichoptera, and 

 Psocoptera, and in each family refers to a different cell!). R. Anterior basal cell 

 (Austen); upper of first basal or radical (Verrall); prepatagial (Lowne). M. Pos- 

 terior basal cell (Austen) ; middle or second basal or radical (Verrall) ; anterior 

 basal (Lowne). Cu. Anal cell (Austen); lower or third basal or radical (Verrall); 

 posterior basal (Lowne). 



