The tube seems to be a metering device, if it was not there the flow rate would have to be much higher, the gear needles get a constant small amount with an extra pusle each time the holes coincide, so the oil pressure is maintained throughout the hollow shaft and tube (and the entire system), and a constant flow is maintained to the end spigot bearing which takes a lot more load as it supports the shaft.
The dog clutches, gears, and other bearings are lubricated by splash, squirt, and oil dragged up from the sump and the 'sumpletts' towards the rear of the casing below the gears.