Preliminary electron microscope observations have shown that in the miracidium of Schistosoma mattheei the surface of the apical epidermal plate consists of branching and anastomosing microvilli. It is suggested that this arboreal arrangement serves to attach the miracidium to the body surface of snail hosts during attempts to penetrate; the apical papilla can therefore be regarded as an attachment organ, functionally analogous to the suckers of the adult schistosome. It is also suggested that the degree of ‘fit’ between the attachment organ and the snail body surface may be an important factor determining the success of attempts by the miracidium to penetrate.

Electron microscopy has also shown that the so-called penetration and apical glands are single flask-shaped cells. No endoplasmic reticulum and very few ribosomes were seen in these cells and it is therefore suggested that, in the mature (free-swimming) miracidium, the “glands” are not functional as such; they are simply sacs full of fluid. If they contain histolytic substances they must either have been synthesized at an earlier stage in the life history of the organism or they are synthesized elsewhere and passed into the “glands”.

Histochemical attempts to identify leucine aminopeptidase and mucin in the contents of the “glands” of S. mansoni miracidia were unsuccessful. It is concluded that these substances probably do not play any role in the penetration into or attachment on snail intermediate hosts by S. mansoni miracidia.