Remarks on the classification of viruses; Small DNA viruses; The papovavirus group; Adenoviruses; Herpesviruses: current information on the composition and structure; Comparative observations on poxviruses of invertebrates and vertebrates; A comparative study of the structure and biological properties of bacteriophages; Picornaviral architecture; Arboviruses: imcorporation in a general system of virus classification; Comparative properties of rod-shaped viruses; Bullet-shaped viruses; Structure and transcription of the genomes of double-stranded RNA viruses; The struture and assembly of influenza and parainfluenza viruses; A plant virus with properties of a free ribonucleic acid: potato spindle tuber virus; The viruses causing the polyhedroses and granuloses of insects; Oncogenic viruses: a survey of their properties.