Egg-shell permeability and hatching of Ascaris suum.

When eggs of Ascaris suum were transferred from glass-distilled water into 0.1--0.4 M NaCl solutions, the water content of the unhatched juveniles fell with increasing concentration of solute. The effect was reversible. The egg-shell was thus permeable to water. The osmotic pressure of the egg fluid was osmotically equivalent to between 0.1 and 0.2 M trehalose. In hatching experiments in Fairbairn's medium containing 0.1 or 0.2 M trehalose, only 5 and 3% respectively of the eggs hatched; 83% of the eggs hatched in the absence of trehalose. The evidence suggests that loss of solutes from the egg fluid permits an increase in the water content of the unhatched juveniles and that this may be responsible for ending their quiescence.