THE INSECT VIRUSES 373 



material, which is greater in bulk than that of normal nuclei, clumps together 

 to form an off-central mass; the remainder becomes attached to the inner 

 surface of the nuclear membrane, to which the central chromatic mass is also 

 apparently attached. Between the two lots of chromatic material a clear ring 

 zone develops, refractive to staining. Later, after the transformation of the 

 central chromatic mass to a network, polyhedra form in the ring zone and 

 grow from about 0.2 to 0.3 to 1 /x or more in diameter, and may even reach 

 10 ix. In the cases of Lymantria dispar and L. monacha, large numbers of virus 

 bundles are accumulated in the ring zone and, as the polyhedra grow, the 

 virus becomes embedded in them. In these two species the polyhedra often 

 originate by deposition of polyhedral protein around aggregations of large 

 numbers of virus particles. As the growing polyhedra begin to pack the 

 nuclei, more and more virus bundles are found inside them and fewer and 

 fewer outside them. 



In infected nuclei of Bombyx mori the course of intranuclear events is 

 somewhat different. In this species, visible virus bundles are not often found 

 in the ring zone and electron microscopy of the virus contents of the polyhedra 

 confirms that the virus rods in this species are almost exclusively in the form 

 of single virus rods. Moreover, immediately prior to the formation of poly- 

 hedra, considerable and increasing amounts of protein material, staining a 

 pale pink with Giemsa and a medium blue with bromophenol blue, is found 

 precipitated in the ring zone. Later, relatively few and very large polyhedra 

 form in the infected nuclei from this protein and leave the nuclear sap free of 

 visible protein deposit. In this species, then, large amounts of polyhedral 

 protein are to be found in the ring zone even before polyhedral formation 

 (Smith and Xeros, 1954a). 



By means of bromophenol blue staining technique, Xeros (1953b) has 

 studied the polyhedra formation in more detail. At about the time of the 

 transformation of the chromatin mass to a network, a great number of 

 propolyhedra appear for the first time in the nucleus. They first appear 

 outside the chromatic network and not as a rule in its pores; the 

 smallest of the propolyhedra observed are about 0.2-0.3 fx in diameter, 

 and are found around the network and at the periphery of the nucleus. 

 These grow into mature polyhedra, 1.5 /x or more in diameter, by 

 which time they pack the nucleus. As the polyhedra grow and begin to pack 

 the nucleus, the nuclear net undergoes further changes. It may expand to 

 embrace a much greater volume of the nucleus and enclose, secondarily, 

 many polyhedra in its enlarged pores. 



Hughes (1953) has studied polyhedral formation in a nuclear disease of the 

 alfalfa caterpillar, Colias philodice eurytheme Bdl. He considers that the 

 polyhedral bodies start as bundles of virus particles enclosed in globular 

 membranes. An elaboration or deposition of some dense material within these 



