Arcturus is the name most closely associated with blue glass valves. This exhibit is a tetrode and dates from 1929 when Arcturus re-designated its type 122 as the 124 to match RCA with the UY224.
The UY-224 was the first USA AC (indirect) heater screen-grid or tetrode
The mesh cylinder is a screen. The sheet metal cylinder anode is seen inside the screen. The oxide coated cathode, filament and filament insulation can be seen at the base of the main electrode assembly. This assembly is the screen grid and this encloses the control grid. The pitch of the screen is smaller than the control grid.
This image taken from the tp shows the relative winding pitch of the inner control grid and close wound screen grid. The control grid support rod can be seen to have an extension clamped on and to this extension is attached the half loop wire connecting to the top cap.
From a slightly different angle the top glass rod support is easier to see. The outer edges of the glass are connected to the outside of the mesh screen as anchor points. One spur from the glass holds the top connection of the heater and this also connects to a wire running down to the pinch. The other spur from the glass rod connects to the control grid for added strength.