Thin sections of polyhedra obtained from gipsy moth larvae infected with P. dispar virus and from silkworm larvae infected with B. mori virus revealed viral particles contained within a pseudohexagonal, macromolecular, paracrystalline lattice. The gipsy moth virus occurs in bundles of one to eight rods enclosed by a limiting membrane. The particles of the silkworm virus, although generally occurring singly, also possess a limiting membrane. The macromolecules appear to be dense, discrete particles when cross-sectioned and to form dense bands by superimposition when longitudinally or obliquely sectioned at certain angles. Calculations of macromolecular size have been made.