The Formation and Function of Mucoids in Virgulate Cercariae, Including a Study of the Virgula Organ

Abstract

The virgula organ of virgulate xiphidiocercariae is primarily a bilaterally paired organ whose parts fuse along the mid-line in some spp. It is the reservoir for secretions from paired unicellular glands arising in the body posterior to the oral suckers of the developing cercariae. Pre-virgula glands empty through individual ducts into the forcibly enlarged oral sucker to form the virgulae. The contents of virgulae are readily hydrolized by inorganic acids or weak bases, possible indications of a mucoidkal nature. Special mucoid differentiating stain techniques confirm the presence of mucins in virgulae, pre-virgula glands, and homologous glands in the cercariae. Observations of emerged living and permanently mounted specimens indicate that mucin discharged from virgulae supplements the weak oral sucker as a means of attachment. Further data, partly inferential, indicate that mucins of non-virgulate glands, and from the virgulae, serve to lubricate the cercariae during pre- and post-emergent migrations in intermediate hosts, and to immunize parasites to the anti-parasite activity of the hosts.