I may perhaps call attention to one or two special points in this work which seem to give promise of further results. The chapter on the Development of the Spinal and Cranial Nerves contains a modification of the previously accepted views on this subject, which may perhaps lead to a more satisfactory conception of the origin of nerves than has before been possible, and a more accurate account of the origin of the muscle-plates and vertebral column. The attempt to employ the embryological relations of the cephalic prolongations of the body-cavity, and of the cranial nerves, in the solution of the difficult problems of the Morphology of the head, may prove of use in the line of study so successfully cultivated by our great English Anatomist, Professor Huxley. Lastly, I venture to hope that my conclusions in reference to the relations of the sympathetic system and the suprarenal body, and to the development of the mesoblast, the notochord, the limbs, the heart, the venous system, and the excretory organs, are not unworthy of the attention of Morphologists. * * * * * The masterly manner in which the systematic position of Elasmobranchii is discussed by Professor Gegenbaur, in the introduction to his Monograph on the Cranial Skeleton of the group, relieves me from the necessity of entering upon this complicated question. It is sufficient for my purpose that the Elasmobranch Fishes be regarded as forming one of the most primitive groups among Vertebrates, a view which finds ample confirmation in the importance of the results to which Prof. Gegenbaur and his pupils have been led in this branch of their investigations. * * * * * Though I trust that the necessary references to previous contributions in the same department of enquiry have not been omitted, the 'literature of the subject' will nevertheless be found to occupy a far smaller share of space than is usual in works of a similar character. This is an intentional protest on my part against, what appears to me, the unreasonable amount of space so frequently occupied in this way. The pages devoted to the 'previous literature' only weary the reader, who is not wise enough to skip them, and involve a great and useless expenditure of time on the part of any writer, who is capable of something better than the compilation of abstracts. * * * * * In conclusion, my best thanks are due to Drs Dohrn and Eisig for the uniformly kind manner in which they have forwarded my researches both at the Zoological Station in Naples, and after my return to England; and also to Mr Henry Lee and to the Manager and Directors of the Brighton Aquarium, who have always been ready to respond to my numerous demands on their liberality.