Apparatus for sex sorting sperm cells contained in a fluid stream according to one or more characteristics of the sperm cells, said system comprising: a flow cytometry apparatus for delivering a fluid stream containing said sperm cells to a first location and for causing the stream to break into droplets at a second location, said flow cytometry apparatus being operable using flow cytometry to classify the sperm cells according to said characteristics and to sort said droplets according to the classification of sperm cells contained in the droplets, wherein the flow cytometer apparatus further comprises a nozzle having an interior surface configured to exert a force on the sperm cells tending to bring them into a desired orientation prior to passing through said beam; and said flow cytometry apparatus comprising an epi-illumination optics system including a focusing lens, said optics system being operable to direct a laser beam through said focusing lens in a forward direction along a beam axis intersecting the fluid stream at said first location so that said sperm cells pass through the beam, resulting in emissions of electromagnetic radiation from the sperm cells directed along said beam axis in a rearward direction, wherein said optics system includes a single photodetector to the rear of said focusing lens for detecting said emissions, wherein said beam is focused by said optics system as a spot on the fluid stream at said first location, said spot having an elliptical shape with a length along a major axis extending at right angles to the direction of fluid stream flow and a width along a minor axis extending parallel to the direction of fluid stream flow, said width being less than the length of the head of a sperm cell passing through the spot. a flow cytometry apparatus for delivering a fluid stream containing said sperm cells to a first location and for causing the stream to break into droplets at a second location, said flow cytometry apparatus being operable using flow cytometry to classify the sperm cells according to said characteristics and to sort said droplets according to the classification of sperm cells contained in the droplets, wherein the flow cytometer apparatus further comprises a nozzle having an interior surface configured to exert a force on the sperm cells tending to bring them into a desired orientation prior to passing through said beam; and said flow cytometry apparatus comprising an epi-illumination optics system including a focusing lens, said optics system being operable to direct a laser beam through said focusing lens in a forward direction along a beam axis intersecting the fluid stream at said first location so that said sperm cells pass through the beam, resulting in emissions of electromagnetic radiation from the sperm cells directed along said beam axis in a rearward direction, wherein said optics system includes a single photodetector to the rear of said focusing lens for detecting said emissions, wherein said beam is focused by said optics system as a spot on the fluid stream at said first location, said spot having an elliptical shape with a length along a major axis extending at right angles to the direction of fluid stream flow and a width along a minor axis extending parallel to the direction of fluid stream flow, said width being less than the length of the head of a sperm cell passing through the spot.