In addition to the principal imaginal discs (cephalic, labial, wing, haltere, leg and genital), the larva in Cyclorrhapha carries as discrete components the rudiments of the imaginal segmental abdominal hypodermis, salivary glands, fore-, mid- and hind-gut, lateral cerebral ganglia and segmental tracheal system (Snodgrass, 1924; Bodenstein, 1950; Shatoury, 1956b; Anderson, 1964, etc.). The embryonic origins of these rudiments have never been firmly established. The present paper describes their origins in the embryo and larva of Dacus tryoni (Frogg.) (Trypetidae), taking a further step in the elucidation of the developmental relationship between the cyclorrhaphan larva and adult.

Material and Methods The embryonic origins of the rudiments in question were traced in serial sections of embryos and larvae prepared by the methods described by Anderson (1962a, 1963b). The reader is referred to these papers for details of the methods employed.

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