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The testicular follicles of the desert-adapted beetle Omorgus freyi (HaaF) (Coleoptera: Trogidae) are unusually large, relative to male size. The advance of the sperm-producing cells towards the efferent duct and, eventually, that of spermatozoa to the deferent duct, is apparently facilitated by the unique structure of these extended follicles. In contrast to the typical insect follicle, those of O. freyi and other scarabaeoid beetles have an internalized and elongated efferent duct. But, additionally, in O.freyi, the follicles are subdivided by longitudinal septa, radiating from the central efferent duct. A net of slow-supercontracting visceral muscles extends throughout the septa and efferent duct. We hypothesize that this unique structure is an adaptation maximizing reproductive potential by mobilizing large numbers of spermatozoa throughout the huge testes and transferring them to the female during the irregular short bouts of reproductive activity following the unpredictable rainfall. (C) 1999 Elsevier Science Ltd. All rights reserved.