Transmission electron micrograph of mouse platelets. Two major granule types are present: the -granules, which are the predominant population (a), and the serotonin-containing dense granule (d) population. Some -granules contain small tubules cut in cross-section (A; arrow, and at higher magnification in [B], arrow) that is probably vWF.67 Others contain a regular fibrillar array, which is probably partially polymerized fibrinogen (C; arrowhead). Although the majority of  granules are round, some have a tent-like shape (D) and a few are very large (E; denoted by asterisk). The platelets shown are GPV-deficient, but indistinguishable granules were also observed in the platelets of wild-type mice.