Who replaced the velites in the princpate army

[Bryan]

so what youre saying is that, in general, the use of light javelins was almost entirely replaced by slings and bows for skirmishing?

I run with the primary sources and what they say. Archers and slingers became an important part of the legion's composition. So a legion consisted of legionaries, archers and slingers, but by the reign of Augustus, this was not the case, a legion consisted of all legionaries. So it was for a short period of time. A legion's archers and slingers could also act separately with javelin men.

What are the sources for all of these claims? 

- 123 BC recruitment of Capite Censi
- Rhodian archers and Balearic slingers being members of Roman citizen legions and not just attached to an army as foederati. Also, were the Thracian cavalry and Ligurian infantry also in he legions too?
- Proof of citizen archers and slingers