Abstract
Electron micrographs are presented which illustrate ultrastructural relationships between the polyhedron macromolecular lattice, polyhedron membrane and condensed fibrous sheets in Spodoptera frugiperda cells infected with Autographa californica nuclear polyhedrosis virus. A fibrous material appears to be implicated in the production of all three structures in the infected nuclei. Fibres within an unorganized network were considered to bind together to form a matrix which became ordered into a macromolecular lattice. Accumulations of fibrous masses seen at the periphery of the polyhedron apparently condensed to form the polyhedron membrane. Single and double condensed fibrous sheets are also found in the nucleus; the ultrastructural studies indicate that they too may have arisen by condensation of the fibrous material.