Abnormal sperm. Coloured scanning electron micro- graph (SEM) showing an abnormal residual cytoplasm (hockey stick) spermatozoon (sperm). This sperm is at an immature stage in its development and so will be unable to fertilize the egg. While all men have some deformed sperm, large numbers may cause male infertility. Sperm defects may be due to a blockage of the epididymis in the testes or to damage to the spermatic ducts, usually caused by a sexually transmitted disease. Varicose veins in the scrotum may also be a factor. Other causes of male infertility include low sperm production and male impotence. Magnification unknown.