Romiti (_Archiv f. Micr. Anat._ Vol. X.) has recently stated that the Wolffian duct develops as an involution from the body-cavity. The fact that the specimens drawn by Romiti to support this view are too old to determine such a point, and the inspection of a number of specimens made by my friend Mr Adam Sedgwick of Trinity College, who, at my request, has been examining the urinogenital organs of the fowl, have led me to the conclusion that Romiti is in error in differing from his predecessors as to the development of the Wolffian duct. The solid string of cells to form the Wolffian duct lies at first close to the epiblast, but, by the alteration in shape which the protovertebræ undergo and the general growth of cells around it, becomes gradually carried downwards till it lies close to the germinal epithelium which lines the body-cavity. While undergoing this change of position it also acquires a lumen, but ends blindly both in front and behind. Towards the end of the fourth day the Wolffian duct opens into a horn of the cloaca. The cells adjoining its inner border commence, as it passes down on the third day, to undergo histological changes, which, by the fourth day, result in the formation of a series of ducts and Malpighian tufts which form the mass of the Wolffian body[45]. Footnote 45: This account of the origin of the Wolffian body differs from that given by Waldeyer, and by Dr Foster and myself (_Elements of Embryology_, Foster and Balfour), but I have been led to alter my view from an inspection of Mr Sedgwick's preparations, and I hope to shew that theoretical considerations lead to the expectation that the Wolffian body would develop independently of the duct. [Illustration: FIG. 8. TRANSVERSE SECTION THROUGH THE DORSAL REGION OF AN EMBRYO FOWL OF 45 H. TO SHEW THE MODE OF FORMATION OF THE WOLFFIAN DUCT. _A._ epiblast; _B._ mesoblast; _C._ hypoblast; _M.c._ medullary canal; _Pv._ Protovertebræ; _W.d._ Wolffian duct; _So._ Somatopleure; _Sp._ Splanchnopleure; _pp._ pleuro-peritoneal cavity; _ch._ notochord; _ao._ dorsal aorta; _v._ blood-vessels.] The Müllerian duct arises in the form of an involution, whether at first solid or hollow, of the germinal epithelium, and, as I am satisfied, quite independently of the Wolffian duct. It is important to notice that its posterior end soon unites with the Wolffian duct, from which however it not long after becomes separated and opens independently into the cloaca. The upper end remains permanently open to the body-cavity, and is situated nearly opposite the extreme front end of the Wolffian body.