Cooperative egg envelope digestion by HCE and LCE. (A) Isolated intact egg envelope. (B) Egg envelope incubated with purified HCE. The egg envelope is markedly swollen and the lamellar structure becomes visible. (C) Egg envelope incubated with a mixture of purified HCE and LCE. The inner layer is dissolved completely, leaving the outer layer undigested. Incubation with purified LCE alone does not produce any significant change in the egg envelope.