The induction of permeability in egg-shells of ascaris-suum prior to hatching

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X-ray micro-analysis was used to study changes in the Na+
content of egg-shells of Ascarissuum. Egg-shells isolated from untreated eggs contained little Na+. In contrast, egg-shells recovered from eggs hatched in vitro in Fairbairn's medium (Fairbairn, D. 1961, Canadian Journal of Zoology 39, 153-162) at 38 °C contained substantial amounts of Na+. Similarly, egg-shells isolated from eggs treated with OI M NaHC03 at 3 °C contained much Na+, as did shells obtained from heat-treated eggs exposed to the same medium. However, free egg-shells treated with 0-1 MNaHC03 containing 0-2 M trehalose bound little Na+. Trehalose appears to prevent the binding of Na+ to the egg-shell and this suggests that the Na+ is not ionically bound by acidic groups. The NaHC03 may, therefore, be bound as an inclusion compound. There is evidence, in the form of blue-black iodine complexes (Barrett, J. 1976, Parasitology 67, 253-262), that the ascarosides of the lipid layer have distinctive binding properties comparable to those of cyclodextrins. Tori formed by ascaroside headgroups in the presence of NaHC03 may provide channels for the escape of trehalose from within the egg prior to hatching.