[Gladular formations in cercariae and the main trends in their evolution]

Hystological studies of glandular formations in 16 species of cercariae were carried out. Their secretion was found to contain acid and neutral mucopolysaccharides, mucins, mucoproteins and elastin. The classification of types of glands is specified. The glands can be of the following types: cystognic case forming, mucoid and glands of penetration. The glands performing uncertain functions and caudal ones are separated into a special group. On the basis of obtained data on the uniformity of chemical compounds of the secretion of glands belonging to different groups their common origin has been suggested. It has been shown that the main trends of the evolution of glandular formations in cercariae depends on the evolution of the life cycle of trematodes.