Abstract
The egg-shell of the ruminant nematode Trichostrongylus colubriformis was composed of outer vitelline, middle chitinous and inner lipid layers. Treatment of eggs with Bacillus thuringiensis israelensis toxin caused disruption of the lipid layer of the egg-shell. Electron-dense blebs were associated with both the lipid layer and outer membrane of the nematode embryo. These ultrastructural changes may be responsible for altered permeability in toxin-treated eggs.