Circuitous-flow electrostatic developer assembly with concurrent axial and circumferential particle movement

An electrostatic latent image developing assembly having a first feed passage for feeding developing material in a first direction, a second feed passage for feeding the developing material in a direction opposite to the first direction. A helical feed screw in the first feed passage, a helical supply screw in the second feed passsage for supplying part of the developing material to a developing sleeve, a connection between both sets of adjacent ends of such feed passages for permitting the developing material to circulate between the passages, wherein the feed screw and supply screw are disposed in parallel relation and the supply screw is provided with buckets around its periphery, the supply screw having a helical blade for advancing developing material in the second feed passage axially thereof while the buckets move the material circumferentially. Preferably, the radius of the helical blade reaches to at least one-half the depth of the buckets.