MUSCULATURE OF DIPTERA — SMART 339 



other indirect flight muscles and is attached dorsally to the posterior 

 region of the scutum and ventrolaterally to the "laterotergite." 



Snodgrass (1935) commented on the great development of this 

 oblique dorsal muscle in Diptera. Its hyperdevelopment in Diptera 

 seems to be a characteristic of the group. The muscle is quite small 

 and of a single fascicle in Telea (Niiesch, 1953) and Panorpa (Has- 

 ken, 1939). 



There is no trace in Anisopus of the third dorsal longitudinal 

 muscle "dims" of various authors. Snodgrass (1935) did not distin- 

 guish this muscle, which is not surprising. This muscle is small in 

 Megaloptera (Maki, 1936), Perla (Wittig, 1955). Periplaneta (Car- 

 bonnell, 1947), Panorpa (Hasken, 1939) and other mecopteroids. 

 It is surprising that Maki (1938) claimed to have found this muscle 

 in Orthellia (Muscidae) ; I have not found it in such Muscidae as I 

 have examined. 



B. STERNAL MUSCLES. 



Other names are: Longitudinal and oblique horizontal ventral 

 muscles (Snodgrass), longitudinal ventral and mesospino-mesof ureal 

 ventral muscles (Maki). 



Maki (1938) was uncertain about these muscles in Diptera; he 

 writes of a "common delicate net of ventral transverse muscles" being 

 present in Diptera. Miller in Demerec (1950) says that sternal 

 muscles are present in Drosophila; Bonhag (1949) records a "very 

 tenuous fibre" in Tabanus. A fine muscle runs from the anterior side 

 of each cup of the mesothoracic furca of Anisopus to the endosternal 

 elements of the prothorax ; they are extremely easily removed, un- 

 noticed, when the gut is stripped out of a dissection. In position 

 these two muscles are on the midline side of the dorsoventral indi- 

 rect flight muscles. 



In Anisopus there appears to be no muscle between the mesofurca 

 and the metafurcal elements. 



These sternal muscles obviously have an important part to play 

 in insects where there is some degree of articulation between the dif- 

 ferent segments of the thorax. It is not surprising that they have 

 become reduced or even lost in Diptera where the prothorax and 

 metathorax have become completely dependent on the very much 

 larger mesothorax. 



