EN
The study lays stress on the morphological variability of metacercariae of Diplostomum pseudospathaceum under the influence of four factors: species and size of the host and density and age of the parasites. A total of 22 experiments were made, using 208 fish belonging to 10 species (three aquarium, seven native Polish species). Ranges of variations found in body size, number of excretory bodies, oral sucker and acetabulum, pharynx, holdfast organ and values of 9 biometric indices are wide and far exceed the ranges of variation given in the literature for this species of metacercaria.