Reflexes are formed in the ommatidium of grasshoppers. Light enters the di-optical region of the ommatidium and reflections are formed in the retinal region. Apposition in bright light and superposition in dim light form reflections. Two processes are described below.Dr. Siddiq Publications
1. Apposition: In bright light each ommatidium can act independently. The iris and retinal sheaths of the ommatidium dilate in bright light. As a result, the crystalline angle is covered. Light rays from the object pass through the cornea directly into the rhabdome. In this case, light rays from the cornea of only one ommatidium reach the rhabdome. The rays of any neighboring ommatidium do not penetrate the rhabdome. A reflex is formed in an ommatidium. In this case the reflection looks like a mosaic floor stone. Hence it is called mosaic reflection.
2. Super position: In dim light, each ommatidium cannot function independently. The iris and retinal sheaths of the ommatidium shrink in dim light. As a result, the crystalline angle becomes uncovered. Light rays from the object enter the rhabdome through the cornea. In this case light rays from the cornea of one ommatidium in addition to light rays from neighboring ommatidiums enter the same rhabdome. As a result a blurred reflection is formed. This is called superposition reflection.