Summon Minion - Types and Numbers

[groshnik]

If a character has Summon Minion, with the +1 Type Extra, that would allow him to summon a variety from a sub-type.
Is he still limited to a single minion, or if one is disabled, he can call one of the other types?
Example: The summoned Panther is disabled. Could he dismiss it and call up the Tiger, or does that require the progression to have more than one? Even though he can only have one summoned at a time?
Is Summon Minion based on 'Minion Slots', progression adding more?

Thanks!