Electron microscopy: selected particles. (a) – (d) Bacteriophage capsids bound to a vesicle via a needle-like extension that is thinner and, with the exception of (a), visibly longer than the T7 tail. (e) A longer-than-tail, needle-like extension-containing capsid not attached to a vesicle. (f) A capsid particle with an apparently broken needle-like extension. The length of the bar is 100 nm.