1. The material of the egg-capsules of selachians and the chorion of trout eggs has been examined by physical, chemical, and histochemical methods.
2. The material of the egg-capsule of selachians has been found to be a quinonetanned protein.
3. The chorion of trout eggs is not quinone-tanned but its formation and chemical behaviour allies it with the invertebrate cuticular proteins rather than with the vertebrate keratins.