this is a gearbox fitted with straight cut gears (and dog engagent BTW) as you can see the gears in the gearbox are cut straight as apossed to



helical gears which are cut at an angle to the shaft!
helical gears place a thrust loading onto the shafts/bearings due to the gears trying to pull/push themself appart! remember that any wasted energy is a waste of power (from the engine)
straight cut gears dont place a thrust loading on the bearing/shafts but they do come at a price! noise

when talking dog in bearbox terms it can either mean dog leg first meaning that first is where 2nd gear normally is on the gear selector (e30 M3's are like this)

or dog engagment gears



as you can see on the faces of these gears there are small drive "dogs" so when selecting between gears these dogs are what engage's the next gear unlike:



syncromesh gear engagment (brass bits) these allow the gear to be selected to match the speed needed before dropping into gear (all standard production cars are like this) and syncro gears shouldnt be rushed (quick shifts a bad idea?)
dog gears will just "bang" in allowing increased gearchange speed, but of cause at the expense of noise and high wear rates

sequential gearbox selection is when you change gear by either pushing or pulling the gearstick (like a motorbike)

this can be done with a barrel on a rathet moving the selector rods!