Abnormal sperm. Coloured scanning electron micro- graph (SEM) showing one abnormal residual cytoplasm (hockey stick) spermatozoon (sperm, top) with two healthy sperm. The residual cytoplasm 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. Magnification unknown.