Fig. 4. Thoracic cross-sections. The Canton-S control fly (A) demonstrates the invariant array of six symmetrical pairs of DLMs (arrows). Sply⁰⁵⁰⁹¹ homozygotes often have missing fibers as represented by this sample (B) that has only four fibers in the left hemithorax and two on the right. Excision of the transposon restores the normal complement of DLMs in most cases, but occasional aberrancies were found, as shown in this Sply^14a homozygote (C). This thorax has an extra (seventh) fiber on the left side (arrow). Thoraces of lace^k05305 homozygotes generally presented with a normal number of DLMs (D), but the morphology was often distorted, owing to the presence of large vacuolar structures that displaced them from their normal positions towards the midline. The addition of either one (E) or two (F) copies of lace^k05305 in the Sply⁰⁵⁰⁹¹ homozygous background restored normal musculature in most cases. With a single copy of lace^k05305, however, DLMs were generally smaller than wild-type fibers.

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