By Schubert Ogden
Hartshorne speaks of "individuals, on no matter what level (particle, atom, cell, vertebrate, human)" ("Freedom as Universal \ [1996\]": 2). Elsewhere in the same essay, he refers to "the singular level of animal, cell, molecule, atom, particle, etc."---evidently —evidently meaning by "the singular level" simply "the level of singulars," which is thus synonymous with "the level of individuals" (7). Wiki Markup
Putting the two passages together, one may say that, on Hartshorne's account, there are at least the following distinguishable levels of individuals or singulars, reading from the lowest to the highest:
particle
atom
molecule
cell
animal
vertebrate
human
September 1997