On the physical identity of scintillons: Bioluminescent particles in Gonyaulax polyedra

The physical identity of the bioluminescent particles (‘scintillons’) extracted from the marine dinoflagellate Gonyaulax polyedra was investigated by electron microscopy and particle counts of the active fractions from sucrose density gradients. Membranous structures are abundantly present in purified fractions, while there is a decrease, relative to activity, in the numbers of guanine crystals, which had previously been implicated as bioluminescent structures. The significance of these findings with respect to the in vivo scinrillon is discussed.