Method for optically determining the sex of fertilized and incubated bird eggs in ovo, including the following steps: - monitoring the passage of time of the incubation up to the formation of at least one identifiable blood vessel (22, 24) or of the heart with flowing blood, - creating a hole in the calcareous shell of the bird egg by means of a hole-producing unit, - searching for the blood vessels (22, 24) forming in the egg or the heart by means of a vision system (13, 13a) and coaxial or lateral illumination with light in the visible wavelength range, - positioning at least one blood vessel (22, 24) or the heart in the laser focus of at least one laser beam source (3; 35, 36), either by moving the egg or by moving an objective lens producing the laser focus, - irradiating the blood vessel (22, 24) or the heart with at least one laser radiation source (3, 35, 36) emitting an excitation wavelength, - registering the backscattered radiation (5, 50, 51, 52) of the irradiated blood vessel (22, 24) or the heart by means of at least one detector, which is connected to at least one evaluation unit, which is connected to an amplification and detector unit connected downstream, wherein a movement of the blood vessel (22, 24) or of the heart out of the laser beam during the registration can take place by way of tracking the blood vessels (22, 24) or the heart or the objective lens, characterized by the following steps: - evaluating the backscattered radiation (5, 50, 51, 52) including the fluorescence radiation (5, 51, 52) in the evaluation unit from the registered spectral intensity of the fluorescence radiation (51, 52) in a spectral range that is red-shifted with respect to the excitation wavelength, wherein the sex-specific properties of the male blood and of the female blood are contained in the intensity and in the spectral profile of the registered fluorescence radiation (51, 52) and wherein at least one of the intensity variables determined from the measured spectral intensities of the fluorescence radiation (51, 52) or their assigned variables with respect to the male blood has an evaluable different value in comparison with at least one of the determined intensity variables or their assigned variables with respect to the female blood in the blood vessels (22, 24) or in the heart, - determining the sex of the bird egg from the difference of at least one of the values of the fluorescence intensity variables (51, 52) or their assigned variables in the evaluation unit, and subsequently at least - displaying the sex of the embryo in the bird egg that has been determined in the evaluation unit. - monitoring the passage of time of the incubation up to the formation of at least one identifiable blood vessel (22, 24) or of the heart with flowing blood, - creating a hole in the calcareous shell of the bird egg by means of a hole-producing unit, - searching for the blood vessels (22, 24) forming in the egg or the heart by means of a vision system (13, 13a) and coaxial or lateral illumination with light in the visible wavelength range, - positioning at least one blood vessel (22, 24) or the heart in the laser focus of at least one laser beam source (3; 35, 36), either by moving the egg or by moving an objective lens producing the laser focus, - irradiating the blood vessel (22, 24) or the heart with at least one laser radiation source (3, 35, 36) emitting an excitation wavelength, - registering the backscattered radiation (5, 50, 51, 52) of the irradiated blood vessel (22, 24) or the heart by means of at least one detector, which is connected to at least one evaluation unit, which is connected to an amplification and detector unit connected downstream, wherein a movement of the blood vessel (22, 24) or of the heart out of the laser beam during the registration can take place by way of tracking the blood vessels (22, 24) or the heart or the objective lens, - evaluating the backscattered radiation (5, 50, 51, 52) including the fluorescence radiation (5, 51, 52) in the evaluation unit from the registered spectral intensity of the fluorescence radiation (51, 52) in a spectral range that is red-shifted with respect to the excitation wavelength, wherein the sex-specific properties of the male blood and of the female blood are contained in the intensity and in the spectral profile of the registered fluorescence radiation (51, 52) and wherein at least one of the intensity variables determined from the measured spectral intensities of the fluorescence radiation (51, 52) or their assigned variables with respect to the male blood has an evaluable different value in comparison with at least one of the determined intensity variables or their assigned variables with respect to the female blood in the blood vessels (22, 24) or in the heart, - determining the sex of the bird egg from the difference of at least one of the values of the fluorescence intensity variables (51, 52) or their assigned variables in the evaluation unit, and subsequently at least - displaying the sex of the embryo in the bird egg that has been determined in the evaluation unit.