Studies on the Formation and Function of Mucoids in Cercariae: Non-virgulate Xiphidiocercariae

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Abstract
Paired, ventral glands, homologous to series descr. in virgulate cercariae, are present in ornate cercariae: Cercaria longistyla and the cercaria of Macroderoides typicus; armate cercaria C. isocotylea; and microcotylous Cercaria alloglossidium corti, and an undescr. micocotylous cercaria from Goniobasis liv-escens. Three pairs of glands anterior and 3 pairs posterior to the acetabulum develop from the base of the oral sucker to the tail stem in all spp. but 1. Only 2 pairs appear posterior to the acetabulum of the spp. from G. livescens. Small glands develop within the oral sucker of C. longistvla. These glands are highly metachromatic to dilute thionin and toluidine blue. Secretions are, therefore, presumptive mucopolysaccharides. A tendency to branch profusely is especially prominent in the glands of C. longistyla and C. macroderoides typicus. Glands appear in relatively immature cercariae, attain max. development in nearly mature cercariae, and discharge before the cercariae emerge from their sporocysts. Discharged secretions are stored in caudal pockets (armate and ornate spp.) and in buccal cavities (micro-cotylous spp.). Discharged after emergence from snails, they assist holdfast activities of cercariae. Discharged mucoids also form a complete layer over the surface of the bodies of cercariae. This film persists on emerged cercariae. It may lubricate migrations through snail and 2d intermediate hosts of the parasites. It most probably protects the cercariae from deleterious immunizing activities of intermediate hosts and from the predictable rigors of hypotonic, free-existence environments.

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