Ultrastructure of the cyst's wall was studied in monocercus type larvae of 5 species of the family Dilepididae: Dichoanotaenia tundra, Particterotaenia porosa, Platyscolex ciliata, Sacciuterina stellifera and Trichocephaloides megalocephala. In all examined cysticercoids the cyst's wall is of identical structure. It differs from the cyst's wall of larvae of the family Hymenolepididae by the character of material filling tegument, by fibrous and muscular, elements forming independent layers, by the absence of myelin-like layer limiting the cyst cavity. In addition to cytons and myofibroblasts in the cyst parenchima there are secretory cells producing electronic dense granules similar to those produced by neurosecretory cells of tape forms of cestodes.