II. The development and growth of the layers of the blastoderm. With Plate 1 29 III. On the disappearance of the Primitive Groove in the Embryo Chick. With Plate 1 41 IV. The development of the blood-vessels of the Chick. With Plate 2 47 1874 V. A preliminary account of the development of the Elasmobranch Fishes. With Plates 3 and 4 60 1875 VI. A comparison of the early stages in the development of Vertebrates. With Plate 5 112 VII. On the origin and history of the urinogenital organs of Vertebrates 135 VIII. On the development of the spinal nerves in Elasmobranch Fishes. With Plates 22 and 23 168 1876 IX. On the spinal nerves of Amphioxus 197 1876-78 X. A Monograph on the development of Elasmobranch Fishes. With Plates 6-21 203 1878 XI. On the phenomena accompanying the maturation and impregnation of the ovum 521 XII. On the structure and development of the vertebrate ovary. With Plates 24, 25, 26 549 1879 XIII. On the existence of a Head-kidney in the Embryo Chick, and on certain points in the development of the Müllerian duct. By F. M. BALFOUR and A. SEDGWICK. With Plates 27 and 28 618 XIV. On the early development of the Lacertilia, together with some observations on the nature and relations of the primitive Streak. With Plate 29 644 XV. On certain points in the Anatomy of Peripatus Capensis 657 XVI. On the morphology and systematic position of the Spongida 661 1880 XVII. Notes on the development of the Araneina. With Plates 30, 31, 32 668 XVIII. On the spinal nerves of Amphioxus 696 XIX. Address to the Department of Anatomy and Physiology of the British Association for the Advancement of Science 698 1881 XX. On the development of the skeleton of the paired fins of Elasmobranchii, considered in relation to its bearings on the nature of the limbs of the Vertebrata. With Plate 33 714