Observations on the Ultrastructure of the Excretory Canal of the Cestode, Spirometra erinacei

The excretory system of the plerocercoid and the adult worm of Spirometra erinacei were studied using transmission and scanning electron microscopes. Attention was concentrated on flame cells, primary excretory ducts, secondary excretory ducts and collecting excretory canals. Special attention was paid to the basic structure of the duct wall with reference to functional morphology. The duct wall was composed of a superficial cytoplasmic layer and a fibrous basal membrane. Bleb-like protrusions were particularly conspicuous in the plerocercoid and in the neck of adult worm, while particles on the duct wall were observed mostly in the mature proglottid of the adult　worm. The significance of these structures are discussed herein. Considering all the characteristics of the fine structure we suggest that the superficial layer of the duct wall is simultaneously functional in the exocytosis-endocytosis cycle and the apocrine secretion.