Type II. Facultative associates. Animals and plants that prey on cockroaches or are incidentally or accidentally picked up by the cockroach, but which can survive or propagate readily on some other host or prey. Steinhaus (1946) emphasized the importance of the environment in determining the type of microbial flora associated with the cockroach which may carry one type of flora in an area which is exposed to filth and a different type in other areas. Because many of these organisms survive passage through or on the cockroach, the blattid may act as a vector of these animals and plants. Group 1. Commensals. (a) Viruses (strains of poliomyelitis virus; p. 103). (b) Bacteria (Enterobacteriaceae, Pseudomonadaceae, Micrococcaceae, etc.; p. 111). (c) Fungi (_Aspergillus_; p. 130). (d) Protozoa (_Iodamoeba_, _Dobellina_, and cysts of _Entamoeba coli_ and _Entamoeba histolytica_; p. 179). (e) Helminths (cysts of various helminths parasitic in vertebrates; p. 208). (f) Arthropods. (1) Mites (_Tyrophagus lintneri_; p. 218). Group 2. Parasites. (a) Bacteria (_Serratia marcescens_; p. 117). (b) Helminths (_Protospirura_ spp.; p. 206). (c) Arthropods. (1) Mites (_Locustacarus_ sp.; p. 219). (2) Insects (_Melittobia chalybii_; p. 248). Group 3. Predators, active. (a) Arthropods. (1) Spiders (p. 214). (2) Scorpions (p. 212). (3) Centipedes (p. 222). (4) Mites (_Rhizoglyphus tarsalus_; p. 218). (5) Insects (dermestids, reduviids, and on occasion adult females of _Tetrastichus_, _Anastatus_, _Ampulex_; p. 234). (b) Vertebrates. (1) Amphibia (p. 269). (2) Reptilia (p. 272). (3) Aves (p. 276). (4) Mammalia (p. 283). Group 4. Predators, passive: Pitcher plants (p. 154). Class B. Associations in which cockroaches serve as commensals or predators. Group 1. Commensal cockroaches. (a) Associates of social insects (_Attaphila_ spp., etc.; p. 315). (b) Obscure associates (p. 316). Group 2. Predatory cockroaches. (a) Interspecies predators (p. 319). (b) Intraspecies predators (p. 322). Class C. Associations of cockroaches with other cockroaches. Group 1. Intraspecies associations. (a) Familial associations (p. 325). (b) Other conspecific associations (aggregations and fighting) (p. 336). Group 2. Interspecies associations. (a) Compatible associations (p. 337). (b) Antagonistic associations (p. 329). Class D. Ecological associations of cockroaches with higher plants. Group 1. Benign associations (p. 139).