MUSCULATURE OF DIPTERA — SMART 351 



posterior levator of the trochanter (13, c) and would appear to act 

 to brace the coxa to the thorax, 



5. THE INDIRECT FLIGHT MUSCLES OF DIPTERA 



It has been recognized for some time (see general texts of insect 

 physiology such as Wiggles worth [1939] and Chad wick in Roeder 

 [1953]) that the indirect flight muscles of Diptera are of a special 

 nature and differ thereby from the other thoracic muscles. Snod- 

 grass (1925) commented on them in his book on the honey bee. These 

 muscles have been the subject of much work recently. The follow- 

 ing comments and references will serve to give the minimum infor- 

 mation immediately needed for the purposes of the present paper, 

 state the position of our knowledge at present, and serve to introduce 

 the reader to the literature if further information is wanted. 



The special nature of their physiology has been investigated by 

 Pringle (1949) who comments further on the matter in his book, 

 "Insect Flight" (1957). They are responsible for the extremely 

 rapid vibrations of the thorax that produce the flight movements of 

 the wings. 



The indirect flight muscles are usually described as being of a 

 fibrous or fibrillar structure ; they give a twitch response to stimuli 

 and are responsible for the extremely rapid thoracic vibrations that 

 give the Diptera their superior powers of flight. Other muscles give 

 a tetanic response to stimuli and are described as tubular. 



Partmann (1948) drew attention to the regularity or semiregu- 

 larity of the division of the great dorsal longitudinal muscles into 

 blocks that, in transverse section, formed a pattern. He suggested 

 that the patterns might have some phylogenetic significance. Tiegs 

 (i955)> who unfortunately only discovered Partmann's paper when 

 his own was in press, made the astonishing discovery that these blocks 

 were in fact giant fibers. Tiegs found a maximum of 230 such fibers 

 in the dorsal longitudinal muscles of Neoaratus (Asilidae) and a 

 minimum of 6 fibers in Rutilia (Tachinidae) and several others. 



Smart (1957) has shown that this giant-fiber type of muscle is 

 not, however, confined to the so-called indirect flight muscles but that 

 the coxosubalar muscle, when present in Diptera, appears to be of the 

 same nature (see elsewhere in this paper). 



6. THE TERGAL DEPRESSOR OF THE TROCHANTER MUSCLE 

 The following names have been applied to this muscle: Tergal 

 branch of extracoxal depressor of trochanter (Snodgrass, 1935, fol- 

 lowed by Miller in Demerec, 1950, and others) ; dorsoventral muscle 



