In the psychropotids the testes are well-developed structures packed with spermatozoa except in those specimens that are infested with protozoan parasites. In the deimatids functional males were never observed. About 50% of the specimens from any population are female but the other half of the population are sexually inactive and are assumed to be predominantly males.The population structure of the species examined is very variable with single modes skewed towards small or large sizes and in some cases a bimodal distribution. Very small specimens were taken rarely in benthic samples although juveniles of Benthodytes sordida and Psychropotes longicauda have been taken in rectangular midwater trawls at distances of 17 to 1000m above the seabed. This suggests the possibility of a pelagic juvenile capable of dispersal by deep-ocean currents and may account for the cosmopolitan distribution of many of these species.