Tetsuya Okino
Department of Parasitology, Kawasaki Medical School, 577, Matsushima, Kurashiki 701-01, Japan.

Abstract
The external morphology of all developmental stages (egg, coracidium, oncosphere, procercoid, plerocercoid and adult worm) of Spirometra erinaceieuropaei (Rudolphi, 1819) Mueller, 1937, was studies by scanning electron microscopy (SEM). The results obtained are summarized as follows: 1) The egg-shell had scattered deep pits on the surface and the pits varied in size from small to fairly large. 2) The surface of free-living coracidium was covered with long cilia and short projections. 3) When the oncosphere transformed into the procercoid, the projections on its surface changed in size and shape to conoid microtriches except the cercomer. 4) The thorn-shaped microtriches were observed only around a frontal pit of fully developed procercoid to early stage of plerocercoid. 5) Microtriches on the body surface in plerocercoid stage were conoid. 6) Filamentous microtriches were restricted to the surface of scolex from 7-day-old plerocercoid to adult worm. 7) In adult stage, digitiform microtriches were observed from neck region to gravid proglottides. 8) Many papillae around the genital atrium of mature proglottides appeared right after it formed. 9) Short digitiform microtriches on the surface of digital end and conoid microtriches on the proximal region of the cirrus were observed.