The characteristics of echinococcal tissue as determined by means of the light microscope have been described by numerous investigators. However, some uncertainties still exist concerning some of the structures observed. Recently, observations made by means of the electron microscope on the fine structure of the adult and larval Echinococcus granulosus (BATSCH, 1786) have been reported by MORSETH (1966, 1967 12 ,13)). Evidently the fine structure of the respective stages of E. multilocularis

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... CKART, 1863 has not been investigated. The present paper reports observations on the structure of the larva of E. multilocularis made by means of the electron microscope. MATERIALS AND METHODS Fully developed larvae of Echinococcus lltiltilocularis LEUCKART, 1863 were obtained from the liver of experimentally infected cotton rats, Sigmodon hispidus SAY et ORD. The tissues were fixed in 6 per cent phosphate-buffered glutaraldehyde at a temperature of about DoC, postfixed in 1 per cent osmic tetroxide (a modification of the double aldehyde-osmium fixation of SABATINI et a1. (1963)), dehydrated in ethanol and propylene oxide, embedded in Epon 812, and sectioned by means of a Sovall MT -1 Porter-Blum ultramicrotome. The sections were mounted on copper grids and stained with saturated uranyl acetate in 50 per cent ethanol solution (WATSON, 1958) , or in a combination of the latter and lead citrate (REYNOLDS, 1963) (10 minutes in uranyl acetate, followed by 10 minutes in lead acetate with brief washing in carbonate-free, glass-distilled water). The preparations were examined by means of the JEM-7 electron microscope. The thicker sections stained with toluidine blue were used to identify the area to be sectioned for electron microscopy. The paraffin sections prepared from the same materials were examined histochemically. RESULTS A Scolex 1 Tegument As determined by means of light microscopy, the cuticle of cestodes IS known to have