They also found that the green-sensitive peripheral photoreceptors function in a similar way as nocturnal Phasmatodea (or stick insects). To protect their eye from direct sunlight during the day, the pigment cell's diaphragm are condensed, and during the night they open fully to allow as much light in as possible. Notonecta glauca have two photoreceptor subsystems: 1. \n* Large and most sensitive peripheral photoreceptors 2. \n* Smaller peripheral and central photoreceptors