The allelomorphscv2 andcv3, but notcv, give rise to abnormalities of the male genitalia. Sixty different types are described. The ductus ejaculatorius was generally absent, the testis and external genitalia rarely so. The average frequency of abnormalities was 23%, but it was shown that the frequency of abnormalities in a family, though not the types found, depends both on genetical and environmental factors. Vasa deferentia were pigmented even when unattached to a testis; unattached testes were spherical or pearshaped.cv2 appears to act on the genital anlage.cv2 females are normal.