Schistosoma mansoni: the structure and elemental composition of pre-acetabular penetration gland cell secretion in pre-emergent cercariae

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Abstract
SUMMARY: The structure and elemental composition of the secretory products of the pre-acetabular penetration gland cells of pre-emergent cercariae of Schistosoma mansoni have been investigated at an ultrastructural level using X-ray probe microanalysis. The secretion contains 2 types of bodies, one homogeneous and one heterogeneous with electron-lucent areas. Using a variety of fixation and sectioning techniques it has been shown that the apparent electron density of the homogeneous bodies (Type B) is the result of interaction with osmium tetroxide and stain. The small electron-lucent areas of the other type of secretory body (Type A) represent regions where granules have been leached out by processing media. X-ray analysis of cercariae still within sporocysts has indicated that these granules are very rich in calcium, and it is suggested that the calcium is absorbed by the developing cercariae through the sporocyst wall from the molluscan haemolymph.