The shape of the photocyte granules ranges from more round to more elliptical, and there are three types of photocyte granules. The bioluminescent reaction is confined to the granules. The granules range from 0.6 to 2.5 micrometers in the larval photocytes of Photuris pennsylvanica and between 2.5 and 4.5 micrometers in the adult photocytes of the asiatic firefly. The size and shape of photocytes can exhibits a great deal of diversity among the species they are found in. The different types of granules have been observed together within individual photocytes. The illumination of the photocytes is confined to the granules where the reaction occurs.