hh⁴/hh^lacZ flies have defects in the external genitalia. In males, the severity of the defects can be classed into 3 types. 20% of males show loss of the anal plates. The typical horseshoe shape of the male external genitalia is maintained with a distinct lateral lobe, posterior lobe and claspers in these flies. In about 20% of males the horseshoe shape of the external genitalia is replaced with an "α" shape, due to the absence of anal plates and a portion of the genital arch, leaving the lateral plates and claspers lying almost close together. Approximately 60% of males completely lack the anal plates and genital arch. The bristles of the lateral lobes, posterior lobe and claspers are fused together and are in the centre of the "α" shaped external genitalia. The penis apparatus shows less extreme defects; hypandrial processes are expanded and the apodeme is defective in approximately 20% of males. In females the external genitalia are less severely affected; the thorn bristles and long bristles of the vaginal plate show duplication, but all other structures are normal.