Fine Structure and Development of the Trematode Integument

Abstract

The integument of the sporocysts, rediae, cercariae, metacercariae, and adult described in this paper is composed of a surface membrane usually separated from a basement membrane by a cytoplasmic layer. The surface membranes of sporocysts, rediae, and developing cercariae possess microvilli and/or irregularities that increase the surface area for absorption. The integument of young cercariae is formed by ceils whose outer cytoplasm becomes confluent to form a continuous layer. Such cells maintain connections with the integumentary cytoplasmic layer through the remaining stages in the life cycle. This layer contains granules, vesicles, and, in some species at least, dense globules that give a positive periodic acid-Schiff (PAS) reaction. In the cercariae of the echinostomes examined and in Parorchis acanthus hollow rods of cystogenous material are formed within certain cells and are moved outward in a less rigid condition to the integument in preparation for encystment. The rod material is PAS-negative. The cyst wall is composed of many lamellae formed principally from the cystogenous rods. The metacercarial integument is richly supplied with small vesicles and mitochondria, the latter confined to the inner half. The cytoplasmic integumentary layer of adult Acanthoparyphium spinulosum contains globules of material that are PAS-, osmium-, safranin-, hematoxylin-, and eosin-negative.