Embryos carrying kn^a.hs show no defects if heat shocked at 37^oC for 1 hour between 4 and 6 hours of development. Most embryos carrying kn^a.hs fail to hatch if heat shocked at 37^oC for 1 hour between 3 and 4 hours of development. Approximately 80% of these embryos develop to the point of making cuticle and consistently show head defects, with a drastic reduction or absence of the lateral graten.