slmoΔ69m1/Df(2L)BSC5 and slmoΔ69m1 homozygous embryos hatch but the resultant larvae are generally sluggish, as measured by the rate of peristatltic contraction, the time taken for on peristaltic wave to travel the length of the body and the time taken to right themselves after being turned onto their backs. As these larvae age, all motion independent of tactile stimulation ceases apart from some motion of the head and mouth parts. Embryonic neuronal development appears normal in slmoΔ69m1 homozygous embryos. Neuromuscular junctions in slmoΔ69m1 homozygous larvae appear electro-physiologically normal.