Fig. 4. Bioassays of the blood from wild-type (wt) and rk⁴ flies showing that bursicon is released by the mutants. Blood was collected donors at either 0 min or 20 min after ecdysis. It was assayed for bursicon activity by injecting into either wild-type or rk⁴ hosts that had been neck ligatured immediately after eclosion. Hatched bars, injection of blood from wild-type into wild-type; black bars, injection of rk⁴ blood into wild-type; gray bars, partial melanization responses.