The high wing beat frequency in insects is intense muscle work, and dependent on a ready supply of ATP. This micrograph of flight muscle from the moth, Phytometra gamma shows the physical relationship between mitochondria and myofibrils. Discrete myofibrils of uniform size are surrounded by large mitochondria (sarcosomes), which may exhibit unusual shapes. In this species, a very dense mitochondrial matrix obscures the numerous closely packed cristae. From J. Auber, C.R. Acad. Sci. (Paris) 264: 621-4, 1967, and reprinted here as Figure 261 from Chapter 7 (Mitochondria) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.