Genre and place in the book. An extended physics of death — the companion of the brief 04-14: there, "you will be received into the seminal reason"; here, how this works at the level of the cosmic "economy of room."
The "there is room" argument. The objection: if souls are immortal, the air would long since be full (as would the earth, with bodies over so many ages). The answer by analogy: as bodies, by dissolution (TERMμεταβολὴ καὶ διάλυσις), make room for new dead, so TERMsouls, after a time in the air, are transmuted, diffused, and "kindled" (ἐξάπτονται), taken up into the seminal TERMreason (λόγος σπερματικός) of the Whole, and make room for newcomers. The reabsorption of the part into the whole is the DOGMAunity of the cosmos (cf. 04-14).
"On the hypothesis that souls survive." A nicety: Marcus offers this conditionally (ἐφ’ ὑποθέσει) — he does not dogmatically assert the immortality of souls. Stoic orthodoxy: souls subsist only until the world-conflagration (ἐκπύρωσις), then are reabsorbed (DL 7.156–157). His point: even granting survival, there is no accumulation — all is transmuted.
The animals eaten. A second argument: count too the number of creatures eaten each day — they are "buried" in the bodies of those who eat them, and there is room, through conversion into blood and changes into the airy and the fiery. All is TERMtransformation; nothing piles up.
Method: matter and cause. The close is a methodological formula: "the inquiry into truth here is διαίρεσις εἰς τὸ ὑλικὸν καὶ εἰς τὸ αἰτιῶδες," the division into the material and the causal-formal. This is the EXERCISEanalytic division of a thing into matter and cause — a recurring move in Marcus (Med. 7.29: "divide every object into the causal and the material"; 12.10: matter, form, purpose).
The disciplines. The principal one is assent: the physical analysis and the matter/cause method. The secondary is desire: the acceptance of one's own dissolution as a recasting into the Whole.
Parallels. Return into the seminal reason, transformation making room — 04-14; 04-05; Med. 8.18; 02-03; 6.24 (Alexander and his groom alike into the seminal reasons, or into atoms). Nothing accumulates: even what is eaten is transmuted into blood, air, and fire — the same transformation principle. Souls subsist until the ἐκπύρωσις — DL 7.156–157; SVF II 809. The division into matter and cause — Med. 7.29; 12.10 (see EXERCISEdefinitio).