5.[+] [Greek: peri kosmou]: _De mundo_: On the universe. [Supposed by
Zeller to belong to the latter half of the 1st century B.C.]
6. [Greek: peri psyches]: _De anima_: On soul, conjoined with organic
body.
7. [Greek: peri aistheseos kai aistheton]: _De sensu et sensili_: On
sense and objects of sense.
8. [Greek: peri mnaemaes kai anamneseos]: _De memoria et
reminiscentia_: On memory and recollection.
9. [Greek: peri hypnou kai egregorseos]: _De somno et vigilia_: On
sleep and waking.