Abstract As the results of my researches in Embryology have all been communicated to the Royal Society, it seems proper to offer to its notice a single observation which I have lately made. On a former occasion I stated that at certain periods an orifice was sometimes visible in the thick transparent membrane (“ Zona Pellucida ’) of the mammiferous ovum ; and that once I had seen an object very much resembling a spermatozoon in the orifice. But spermatozoa, so far as I am aware, have never been described as seen within the ovum of any animal. I t may therefore be interesting to physiologists to be informed that about a fortnight since, in examining some ova of the Rabbit of twenty-four hours, from the Fallopian tube,— in which the orifice above-mentioned was no longer visible,— I unexpectedly discerned a number of spermatozoa in their interior. These ova were submitted to the inspection of Professor Owen, and I after­ wards showed one of them to Professors Sharpey and Grainger, all of whom agreed that the spermatozoa were contained within the Ovum