The mode of hatching of the egg of Fasciola hepatica II. Colloidal nature of the viscous cushion

1. 1. A viscous and granular cushion of material at the opercular end of the fully developed egg of Fasciola hepatica expands within the egg just prior to the release of the operculum during normal hatching. This expansion is shown to play a passive role in the hatching phenomenon. 2. 2. The cushion resembles a colloid and consists at least in part of protein. It changes from a contracted gel to an expanded sol with changes in the ion constitution of the fluid bathing it. 3. 3. Evidence is presented to show that expansion of the cushion within the unhatched egg is accompanied by osmosis of salts or other materials from the egg. This exosmosis is believed to result under natural conditions from damage to or destruction of the vitelline membrane by the direct or indirect action of the hatching enzyme. 4. 4. Expansion of the cushion within the egg can be artificially induced by exposing the egg to heat or to toxic solutions. This change provides a valuable visual clue to the penetrability to toxic materials and may play a useful role in ovicide research.