62 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 



but I.eydig, Graber and others suggest that the}' may have an auditory 

 function and other functions have been ascribed to them by recent 

 in\estigators.''' Internal, so-called chordotonal organs, and external 

 sensory protuberances with transversely sculptured surfaces, occur in 

 the basal region of halter (scabellum) ; and the halteres of most Nem- 

 atocera are covered with so-called sense hairs, although these are 

 largely restricted to the capitellum in the higher Diptera. 



The halteres ai-e absent in some degenerate parasitic forms and 

 they are occasionally atrophied in some tipulids, mycetophilids, 

 stetho})athids, etc., but they are usually retained even when the wings 

 are lost, and apparently play an important role in the general make- 

 up of tlie insect. 



8. The lags 



The front, middle and hind legs (or the legs of the pro-, meso- 

 and metathorax) are referred to as the pedes antici, medii and postici 

 by Verrall (1901), who insists that the designation anterior legs (pedes 

 anteriores) should include both the fore and middle legs, rather than 

 the fore legs alone, and that the designation posterior legs (pedes 

 l)osteriores) should include both the middle and the hind legs, instead 

 of the hind legs alone. Thus, according to Verrall, there is only one 

 j)air of front, middle or hind legs, while there are two pairs of an- 

 terior or posterior legs according to his terminology; and he applies 

 the same usage to the parts of the legs, such as the femora, tibiae and 

 tarsi, as well. Verrall's suggestion, however, has not been accepted by 

 most dipterists. 



Various methods of designating the different surfaces of the legs 

 have been proposed by Schnabl (190t)), Stein (1903), and other dip- 

 terists, but the method which has been followed by most dipterists is 

 that suggested by Grimshaw (1905). If the legs be thought of as 

 though they extended parallel to each other and perpendicular to the 

 median plane of the body, with the tibia and tarsus as nearly as pos- 

 sible in a straight line with the femur, it will be readily seen that 

 each leg has an anterior, posterior, dorsal and ventral surface. The 

 surface between any two of these four principal surfaces is designated 

 by a combination of the names of the two surfaces concerned. Thus 

 the antero-dorsal surface is the one between the dorsal and anterior 

 surfaces; the antero-ventral surface is the one between the anterior and 

 ventral surfaces; the postero-ventral surface is the one between the 

 ventral and posterior surfaces; and the postero-dorsal surface is the 

 one between the posterior and dorsal surfaces. A combination of these 

 gives eight surfaces for the leg. Looking down on the right side of 

 the insect's body, with its head to the right, and with its legs extended 

 at right angles to its body, the following sequence is passed through 

 in working around the leg, starting at tlie top, and following a clock- 

 wise sequence, namely: the dorsal, antero-dorsal, anterior, antero- 

 ventral, ventral, postero-ventral, posterior, and postero-dorsal sur- 



4n^" wJ«L^"i^a?ol-'°'^''.^l?^^^' ^^^ halteres may be regarded 

 rfin t./T°^^''^' "^^^' ''"'* ^^® stimuli of their rapid vibrations 

 tain the tone or vigor of the active muscles of flie-ht 



as "stimulatory or- 



may serve to main- 



e muscles of flight. 



