Ezri Dax summons Joran, a former host
The Rite of Emergence was a Trill rite that was performed by a joined Trill to bring forth the personality and memories of a previous host. This personality can then be interacted with by the current host.
This rite was used in 2375 by Ezri Dax to bring forth Joran Dax to help her investigate a number of mysterious deaths on board Deep Space 9. (DS9: "Field of Fire")
The Rite of Emergence was very similar to the Trill zhian'tara ritual, except the zhian'tara telepathically used other people's bodies as vessels and the Rite of Emergence solely took place in the host's mind. (DS9: "Facets", "Field of Fire")
Robert Hewitt Wolfe, who wrote "Field of Fire", once described the Rite of Emergence as "Trill mumbo-jumbo." (Star Trek: Deep Space Nine Companion, p. 649)