an eye having a single lens
(plural: stemmata): Simple eye of a caterpillar, usually arranged in a group of six on each side of the head (see Figure 3).
(pl. stemmata) The light sensitive organs found in lepidopterous larvae. Each stemma consists of multiple photo receptor cells, all receiving light through a single lens. See ocellus.
A stemma (pl. stemmata) is a simple eye in some insect larvae. It is also called a lateral ocellus.