The general occurrence of intramitochondrial crystals in Hydra cells.

Intramitochondrial crystals are found in normal Hydra as well as in animals undergoing various conditions (budding, regenerating, eserine-treated, and sexual). They appear in all regions of the animal, but seem to be more prevalent at or near the extremities: hypostome, tentacles and basal disk. They are found in all of the seven basic cell types: interstitial, cnidocyte, nerve, epithelio-muscular, gland, mucous and digestive cells. The chemical nature of the intramitochondrial crystals is unknown and their significance remains speculative.