What does it mean if a quotation contains three spaced periods enclosed by brackets

1. saved aronnax from drowning "an incident" 2. speed of the nautilus man-of-war 3. next to captain nemo conseil 4. electricity vigo bay 5. "a coral tomb" 20,000 leagues 6. the nautilus runs aground nemo's "thunderbolt" 7. episodes are connected by aronnax's quarters 8. captain nemo's "bank" cause 9. distance aronnax traveled on the nautilus "a fine death for a sailor" 10. captain nemo sinks for revenge 50 miles per hour