Observations on effects of ultra-violet rays upon living eggs of Nereis limbata exposed before insemination.

A. Eggs ofNereis exposed to ultra-violet light before insemination exhibit threee marked effects: 1. They extrude jelly equally from all parts of the cortex. 2. The first cleavage plane passes through that area of the egg from which the membrane is farthest removed-the site of maximum effect of the exposure. This sharply localized cortical injury can be traced throughout the egg's development into the worm of three segments. The majority of these worms exhibit a blister on the side of the first segment behind the head. 3. Polar body formation is suppressed. B. These effects are due to a sharply localized cortical injury.