In this memoir the author described the dissection of the gravid uterus of an Orca gladiator, for which he was indebted to Mr James Gatherer of Lerwick. The paper contained an account of the uterus and appendages, the fœtal membranes, the position and general form of the fœtus, and a comparison of the placentation with that of other mammals possessing the diffused form of placenta. The structure of the uterine mucous membrane, its subdivision into a gland layer and a crypt layer, the relations of the glands to the crypts, their structure, the arrangement of their blood-vessels, and the much greater vascularity of the crypts than of the glands, were especially described.