The crankcase ventilator has been disabled.
I wonder if they removed the impeller, as well (from the drive end of the governor)?
At some point it was determined they were not needed.
They pulled air from the intake tube, (after the air filter) and pushed crankcase gasses out the vent tube (the opposite of how most PCV systems work).
NOT sure why they were eliminated in later tractors, and often disabled in older units, but it PROBABLY has to do with the advent of better/modern detergent oils that help eliminate sludge buildup.