The formation, structure, and histochemistry of the metacercarial cyst of Philophthalmus gralli Mathis & Léger

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Abstract
The presence of three types of cystogenous gland cells, designated as protein, mucopolysaccharide, and mucoprotein cells, in P. gralli cercariae has been demonstrated.The protein cells are PAS-negative but positive for tyrosine-, histidine-, and arginine-containing proteins. No tryptophane is detectable in this type of cell. The mucopolysaccharide cells are positive for acid mucopolysaccharides and are gamma-metachromatic. The mucoprotein cells are PAS-positive and diastaseresistant.The mechanism of metacercarial cyst formation is described. The fully formed cyst consists of three walls designated inner, middle and outer walls. The outer wall is subdivided into a basal and a peripheral layer.Histochemical studies on the cyst walls have shown that the outer and middle walls are PAS-negative but the inner wall is PAS-positive and diastase-resistant. All the walls include proteins but differ in their amino acid contents.By comparing the chemical composition of the cyst walls with that of the three types of cystogenous gland cells, it is evident that each cyst wall is formed from the secretions of two or more types of cells. The outer and middle walls appear to be formed from the secretions of both protein and mucopolysaccharide cells, and the inner wall from protein, mucopolysaccharide, and mucoprotein cells.This research was supported in part by a grant from the American Cancer Society.