A histopathological study of granulosis virus diseases of the spruce budworm, Choristonezira fumiferana Clem., the larch budworm, Eucosnta griseana Hbn.,and the imported cabbage worm, Pieris rapae Linn., has shown that the viruses may infect fat, hypodermal, tracheal matrix, and blood cells. The viruses multiply and develop within the cytoplasm of these cells appearing first as spheres and then as rods. Finally each rod becomes occluded by protein to form a "granule". 1bIanuscri~t received F e b r~~a r v 24. 1958. ~o n t r i b u f i o n No. 451, from fhe ~i v i s i o n