Curtis on the other side contended that Andromeda and other such "nebulae" were separate galaxies, or "island universes" (a term invented by the 18th-century philosopher Immanuel Kant, who also believed that the "spiral nebulae" were extragalactic). He showed that there were more novae in Andromeda than in the Milky Way. From this he could ask why there were more novae in one small section of the galaxy than the other sections of the galaxy, if Andromeda were not a separate galaxy but simply a nebula within Earth's galaxy. This led to supporting Andromeda as a separate galaxy with its own signature age and rate of nova occurrences. He also cited dark lanes present in other galaxies similar to the dust clouds found in Earth's own galaxy.