Sac-like structures at the extremities of an epidermal pseudotumour on a live specimen of Pseudopleuronectes obscurus and X-cells released from the sacs in tissue culture plates. a & b) Appearance of a fresh epidermal pseudotumour showing sac-like structures that can be separated from the main part of the pseudotumour intact, black arrows indicate the same sac attached and detached in a & b respectively. c) X-cells and host tissue debris immediately after being released from a sac-like structure. d) X-cells maintained in plastic tissue culture plates containing seawater, 24 hrs after being released from a sac-like structure. Scale bars a = 10 mm, b = 2 mm, c = 20 μm, d = 10 μm.