What's the pump ontop of the transfer case?

[ChiGGz]

I took it out and noticed a rubber bulbish thing on the top of the xfer case. Looks like a pump. What's this for? And why is the bulb part detachable from the nozzle that goes into the transfer case?

 

[The_EE]

Its a breather. Put it back in or your transfer case will suffocate.

 

[cruisintalonawd]

Its a breather. Put it back in or your transfer case will suffocate.

I think thats the funniest thing I've read all day.....but ya leave it on there