What is this brass nub on my Mikuni BS38 carb?

We are trying to figure out what the heck these brass tubes are on the side of the carb. Do they need to be plugged? Should a vacuum hose be on them?

I think that's the bowl vent line. The big brass on the side is fuel inlet, the small brass fittings on the bottom of the float bowls are overflow tubes.

Your bike will run without hoses on the vent nipples but the hoses keep junk from falling in and slow fuel evaporation.