Oncosphere formation

Stage 7 Oncosphere formation. Characterised by the appearance, in the uterus, of embryonated eggs containing fully formed hexacanth embryos. 

This envelope is a syncytial layer involving two cells Ailing the space between the embryo and the egg shell it is responsible for the formation of the embryophore and oncospheral membrane (204). After the latter is formed, what is left of the inner envelope becomes the cytoplasmic and gelatinous layers-zones I and II, respectively, in H. diminuta (Fig. 7.14). The latter has the ability to swell readily in dilute salt solutions, a property which may facilitate the escape of the oncosphere during hatching (p. 191) (442). 

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