Vacumatics - see-through barrel and vertically striated bodies
The major novelty of the Parker Vacumatic Line is probably that the part of the pen body closest to the section is transparent, thus letting the writer know how much ink is left in the pen (see pic below). Another novelty is the filling system that uses a redesigned rubber sach system allowing for much more ink in the pen. Hence the name: Vacumatic.
The Vacumatic Line was introduced in 1933, and it replaced the Duofold Line as Parker's top of the line pen. Initially, until around 1940, the Vac Line consisted of two branches; a deluxe line with two-toned nibs, see below) and striated 'jewels' (top of cap and closing of bottom). To the left you can observe the striated jewel on the green striped cap. The economy line was without these features.
Of course the pens came in different sizes. The caps to the left belong to maxima or senior sized pens (or simply over-sized pens), but you could also get standard sized pens and smaller sized pens.
And of course the Vacumatic Line saw a lot of more or less important changes during the span of production that ran from 1933 until the end of the 1940s (and even longer in some countries). But note that already in the beginning of the 1940s, the Vacumatic was replaced by the Parker 51 as top of the line pen. Vacumatics: A pleasure to look at and to use, and quite annoying to repair! (But then, as stated elsewhere, I'm not a good repairman, so don't blame the pen).