Studies on molluscan schistosomiasis: An analysis of the development of the cercaria of Schistosoma mansoni

Development of cercariae within intramolluscan germinal sacs is recognized to be in seven stages; in brief, these stages are: 1, germinal cell; 2, naked cell aggregate; 3, germ ball prior to elongation; 4, elongating germ ball; 5, tail bud stage; 6, tail elongation stage; and 7, fully developed cercaria. Schistosoma mansoni cercariae at each of the developmental stages is described. The dimensions of both germinal and somatic cells comprising the bodies of developing S. mansoni cercariae decrease with maturation. The surfacial membrane of Stage 3 cercarial embryos is formed by a number of small somatic cells which migrate to the surface and coalesce. The chronologic and partially synchronized development of S. mansoni cercariae is presented. The body-tail ratio during S. mansoni cercarial development is presented.