The protozoa of _Cryptocercus_ can be transferred from one individual to another (Nutting and Cleveland, 1954). They can also be transferred to the termite _Zootermopsis_ where they survive only until the host molts; the reverse is also true, _Zootermopsis_ Protozoa can survive in _Cryptocercus_ until the cockroach molts (Nutting and Cleveland, 1954a). VI. VIRUSES ASSOCIATED WITH COCKROACHES Annotations on some of the following observations may be found in Roth and Willis (1957a). Use of asterisk is explained in footnote 3, page 4. POLIOMYELITIS VIRUSES * =Lansing strain= _Experimental vectors._--_Blattella germanica_, U.S.A. (Hurlbutt, 1949, 1950). _Periplaneta americana_, U.S.A. (Hsiang et al., 1952). * =Brunhilde type, Minnesota and Mahoney strains= _Experimental vectors._--_Periplaneta americana_, U.S.A. (Fischer and Syverton, 1951; Syverton et al., 1952). * =Columbia SK virus= _Experimental vectors._--_Periplaneta americana_, Great Britain? (Findlay and Howard, 1951): Results with _Blattella germanica_ were negative. * =Four unspecified strains= _Natural vectors._--_Blattella germanica_ and/or _Blattella vaga_, _Periplaneta americana_ and/or _Periplaneta brunnea_, and _Supella supellectilium_, U.S.A. (Syverton et al., 1952; Dow, 1955; Dow _in_ Roth and Willis, 1957a). OTHER VIRUSES * =Coxsackie viruses= _Experimental vectors._--_Periplaneta americana_, U.S.A. (Fischer and Syverton, 1951a, 1957): Recently Fischer and Syverton (1957) found that after feeding a single meal of Coxsackie virus to _Periplaneta americana_, the gastrointestinal tracts of the insects, which were removed at 5-day intervals up to 20 days, contained sufficient virus to paralyze and kill test mice. Cockroach salivary glands, removed 5 days after the insects had fed, contained the virus which caused paralysis and death in test mice; mice were also infected by virus obtained from salivary glands removed from the insects 10 and 20 days after the cockroaches had fed once on the virus. The virus was also isolated from the cockroaches' feces and rarely from the fat bodies and reproductive organs. Fischer and Syverton concluded that it is possible that cockroaches could acquire the virus, by feeding on mammalian excreta, maintain it for a period of time, and transmit it by contamination of food. The virus could also be transmitted through the feces of wild mice if the mice happened to feed on virus-infected cockroaches. * =Mouse encephalomyelitis virus= _Experimental vectors._--_Periplaneta americana_, U.S.A. (Syverton and Fischer, 1950). * =Yellow-fever virus= _Experimental vectors._--_Blattella germanica_, Great Britain? (Findlay and MacCallum, 1939). VII. BACTERIA ASSOCIATED WITH COCKROACHES