Observations on the living eggs of the rabbit

In the course of certain observations on the fertilisation of rabbit ovain vitro it soon became evident that, contrary to normal expectation, unfertilised ova will undergo varying degrees of development, much of the development being indistinguishable morphologically from the development of fertilised ovain vivo . It was decided, therefore, to undertake a comprehensive study of the history of tubal ova and of their behaviourin vitro . Advantage was taken of the fact that the rabbit ovulates regularly at about 10 hours after copulation (e. g. , Heape, 1905; Hammond and Marshall, 1925; Walton and Hammond, 1928) to obtain ova of known age. Unfertilised ova were obtained by mating non-pregnant rabbit does to vasectomised bucks, and the eggs liberated from the ovary were recovered from the tubes by washing them out with sterile isotonic Pannett-Compton solution (Pannett and Compton, 1924). By this method eggs were obtained from the tubes from 11 to 72 hours after copulation. Between 72 and 96 hours after copulation the unfertilised ova enter the uterus and similar uterine washings were made to recover such eggs. Each doe used was mated to two or three vasectomised bucks. That these animals had been successfully operated upon and were incapable of ejaculating spermatozoa was already shown by the fact that no spermatozoa were found in smears taken from the vulva of the doe immediately after copulation and eggs obtained from these matings never showed the characteristic features, to be described later, of normally fertilised eggs. Some, moreover, showed no evidence of developmentin vivo . Ova fertilisedin vivo and used for control experiments were similarly obtained, but from matings made to normal fertile bucks. To obtain the uterus and tubes the doe was killed and these organs removed with the ordinary precautions for attaining sterile conditions. In the few experiments in which ovarian ova were employed the eggs were obtained by pricking ripe follicles with a sterile needle and floating the emerging eggs into sterile Pannett-Compton solution.