An apparatus for producing a body, preferably a nano-body, through the introduction of a body-forming fluid into a dispersion medium. The apparatus includes: a fluid housing configured to house a dispersion medium; at least two separated flow paths along which the dispersion medium flows in a laminar flow, at least two of the separated flow paths converging at a flow-merge location; a fluid flow arrangement which, in use, causes the dispersion medium to flow along each flow path to the flow-merge location; at least one fluid introduction arrangement located at or proximate the flow-merge location configured, in use, to feed the body-forming fluid into the dispersion medium; and a flow constriction arrangement proximate to or following the flow-merge location, which in use, constricts and accelerates the dispersion medium flow proximate to and/or following the flow-merge location.