ULTRASTRUCTURE OF THE ATYPIC MUSCLES ASSOCIATED WITH TERMINALIAL INVERSION IN MALE AEDES AEGYPTI (L)

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Abstract
Rotation of the terminal abdominal segments of adult male mosquitoes was accomplished by the action of 2 pairs of small crossed muscles (dorsal and ventral sets). These develop from intersegmental myoblasts between abdominal segments 7-8 during the pharate adult stage, the origins migrate laterally to give the crossed arrangements, and the muscles do not contract until after adult emergence. Similar muscles were not found in adult females. One member of each crossed set begins to contract soon after adult emergence, continues contraction, then supercontracts over a period of about 20 h to reach a final length only 25% the initial length. The contracted muscles contract only once and remain in this state locking the rotation in place. The other member of each crossed set becomes stretched to 2.5.times. its original length, it never shortens, and it disappears within a day. The ultrastructural details of these muscles are different to those described for other slow and atypical insect muscles.