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Microfilariae are taken up with the blood meal and, on entering the stomach, the microfilaria casts its sheath in 3 h and, piercing the stomach wall, enters the thoracic muscles and fat body of the thorax, but principally that of the abdomen. Development is complete in 10 days. In 3 days, it becomes broad and torpedo shaped; on the fourth and fifth days the squat form lengthens to 0.8–1 mm; on the sixth day the corkscrew-like appearance is replaced by gentle curves. Then the first ecdysis occurs and the sharp tail is replaced by a rounded, trilobed extremity. By the 10th day it measures 2 0.025 mm and two moults have occurred, and infective third-stage forms migrate forward into the head where they accumulate in large numbers, the majority at the root of the proboscis. At the next feed they break out of the labium and make their way on to the surface of the skin, which they penetrate, and migrate along the interfascial planes.

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Development of L. …