The arrangement patterns of nucleocapsids within the envelope of \%Autographa californica\% nuclear polyhedrosis virus were studied by electron microscopy. Numbers of nucleocapsids observed in an envelope in their cross sections ranged from 1 to 17, and the frequencies at 2,3,4,5,6 and 7 nucleocapsids were significantly higher than the others, suggesting that these numbers of nucleocapsids were more commonly involved in an envelope. The regular arrangement patterns of nucleocapsids within envelope were observed in cross sections. Envelope outlines can be classified into a triangle (3 nucleocapsids in an envelope),lozenge and square (4 nucleocapsids in an envelope), trapeziun (5 nucleocapsids in an envelope), pentagons (5 or 8 nucleocapsids in an envelope) and hexagons (7 or 10 nucleocapsids in an envelope). The irregular arrangement patterns of nucleocapsids within envelopes were also observed in cross sections.
