The distinguished French naturalist, Professor H. Milne Edwards, in the ninth volume of his valuable Lectures on Comparative Anatomy and Physiology, published only last year, when referring to the fœtal membranes in the Cetacea, states, that much information is still required to complete our knowledge of that subject.It may perhaps be advisable, before I commence to describe the results arrived at by my recent dissections, to give a brief account of the observations made by previous inquirers into this department of anatomy, so that we may more clearly recognise wherein our deficiencies lie, and the direction in which our researches ought to be conducted, in order to render our information as complete as possible.