1. Evidence is brought forward to show that the sterility of the male and female hybrid pheasants is due to abnormalities occurring at the synapsis stage of the reduction division. 2. The spermatozoa of the hybrids are either deformed, with chromatic beads and thickenings on them, or else of abnormal size, double-sized spermatozoa being of frequent occurrence as in hybrid pigeons. The oocytes in the hybrid females fail to grow owing, probably, to the early synapsis which should take place in the 19 day old embryo having gone wrong. 3. Partial assumption of cock’s plumage by the female as the result of ovarian degeneration is shown to be of fairly common occurrence. The oviduct in these cases may be either atrophied or greatly hypertrophied. Assumption of hen’s plumage by the cock bird is much rarer and is generally due to hereditary transference of this character independently of any disturbance of the testes or the reproductive function. 4. The sex-ratio among hybrid pheasants gives a large preponderance of males over females (228 ♂ to 135 ♀). This preponderance cannot be accounted for by a greater death-rate of female chicks in the shell or subsequently, and must be presumably due to a selective fertilisation by which more male zygotes are produced than female, or else to a selective death-rate at so early a stage of developement that no trace of an embryo could be detected.