19th Century practice of calling new missionaries

[Duncan]

I know in the 19th Century the Brethren would read lists of names of men to serve missions at General Conference. I am assuming too that most of those called were surprised that their name was read, unless they applied for it? But does anyone know more about this practice, did people apply for a mission like they do now or when and why did this practice stop? Thank you!

[JAHS]

Here are a few sources that refer to this activity of calling missionaries at Conference:

"The early missionaries of the Church went forward, beginning with Samuel H. Smith, only a few days after the Church was organized. 
After the Saints arrived in the valley, it was not an uncommon thing to have read long lists of names of men attending the general conference of the Church who were called to go into the mission field and carry the message of the restored gospel. In later years it became the custom to issue the calls by letter."  TEACHINGS OF EZRA TAFT BENSON by Ezra Taft Benson

"In the latter part of February 1831, the Prophet received a revelation instructing the elders to gather in Kirtland in June for a special conference. One of the purposes of this missionary gathering was also revealed by revelation: All elders who were worthy and able were to "go forth into the regions round about, and preach repentance unto the people."
At a conference in Kirtland in June, twenty-eight men, including the Prophet, received specific missionary callings. By revelation, these elders were called and instructed to travel to Missouri, two by two, taking different routes and "preaching the word by the way."  
HEAVENS RESOUND: A HISTORY OF THE LATTER-DAY SAINTS IN OHIO, 1830-1838 by Milton V. Backman

"The conference in June 1831 saw the naming of twenty-eight elders by name; they were told who was to travel with whom as companion, where to go, and general directions about route. 31 This kind of supervision continued to be exercised by the Kirtland leaders, usually through the High Council.  In early 1832, for example, Jared Carter went from Amherst into Kirtland to find out his assignment, viz. where he should go to preach and who would be his companion. During 1833-34 licenses were issued to these traveling elders by either the Missouri or the Kirtland High Council."  BYU STUDIES, VOL. 11 (1970-1971)  Kirtland as a Center of Missionary Activity, 1830-1838 by Davis Bitton

It appears that in the early days of the church elders didn't have to apply to serve. Anyone who was a worthy elder was fair game and indeed expected to serve somewhere as a missionary without any warning that they were going to be called. They were called either at a General conference or by letter.
Not sure when prospective missionaries had to start sending in applications to be called.