Chelal growth in pseudoscorpions

There is a linear relationship between the successive positions of named trichobothria on the pedipalpal chelae during the course of post‐embryonic development of five British pseudoscorpions belonging to the family Neobisiidae. Growth constants calculated from the trichobothrial data are higher than those calculated for the chelal axis. This discrepancy is resolved in terms of a model, based on growing and non‐growing regions, which is a good approximation to the data. The extent of these regions is calculated for all stages and differences between the species are noted. The assumptions implicit in the model, its realism and its predictive value are discussed.