LONDON. Royal Society, Jan. 27.–S. A. Asdell and F. H. A. Marshall: The effect of the ovarian hormone in producing pro-cestrous development in the dog and rabbit. Injections of follicular extract obtained from solution in alcohol produce typical pro-cestrous changes in the uterus of the bitch and of the rabbit during the ancestrous period (that is, at a time when the uterus is normally quiescent). There was also a growth of the vaginal epithelium, followed by a breaking down of the cornified cells. No definite cestrus was produced, so that in the actual production of cestrus a further factor may be involved.