The peritrophic membrane and faecal pellets of Gammarus lacustris limnaeus Smith

SUMMARY. Gammarus lacustris limnaeus Smith was fed decomposed autumnshed leaves of maple ( Acer saccharum Marsh.) and poplar ( Populus tremuloides Michx.). Faecal pellets were collected at various time intervals after egestion and examined under a light and a scanning electron microscope. Nearly all the faecal pellets collected up to a period of about 7 h after egestion possessed a thin, tightly-fitting peritrophic membrane while those that had been outside the gut of the animal for a longer time lacked a peritrophic membrane. Presumably, after egestion faecal pellets swell because of absorption of water leading to eventual rupture and loss of the membrane. The surface of newly extruded pellets is devoid of microbes and microbes seem to play a very insignificant role in the loss of peritrophic membrane from the pellets.