Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Male sterility in Ink4c Ink4d doubly deficient mice: hematoxylin and eosin staining of sections of 6-month-old epididymes from wild-type (top) and Ink4c Ink4d double-null (bottom) male mice. The wild type was replete with mature spermatozoa, while the double-null epididymes had fewer to no spermatozoa. Magnification, ×200. (See related article on page 3244.)