Compound eyes fall into two Groups.

http://en.wikipedia.org/wiki/Eye

Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image.Compound eyes are common in arthropods, and are also present in annelids and some bivalved molluscs. Compound eyes, in arthropods at least, grow at their margins by the addition of new ommatidia.