Complex sentence: It does this through the use of a series of narrow channels or "fissures" along its lower edge: as ink flows down these fissures, air is simultaneously allowed to flow upwards into the reservoir in an even exchange of volumes.
Split into simpler sentences: It does this through the use of a series of narrow channels or "fissures" that run down its lower edge. As ink flows down these fissures, air is simultaneously allowed to flow upwards into the reservoir in an even exchange of volumes.