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V I I I .-O n the Calcification o f the Vertebral Centra in Sharks and R ays.

This paper furnishes descriptions of five skulls of fœtal Whales—three of Megaptera and two of Balœnoptera . The investigation was begun in July, 1912, at the British Museum (Natural History), but was discontinued, partly in consequence of the pressure of other work, and partly owing to the superior attraction of Cephalodiscus as a subject of research; it was resumed in November, 1920, in the Huxley Research Laboratory at the Royal College of Science. My thanks are due to Sir Sidney F. Harmer, Director of the Natural History Departments of the British Museum, for permission to prepare and describe the skulls; also to Prof. E. W. MacBride, and the administrative officers of the Royal College of Science, for the facilities offered by the Huxley Research Laboratory for the prosecution of the Research. For frequent hints and suggestions during the progress of the work, and for much valuable advice, I am indebted to Sir Sidney Harmer, Prof. E. W. MacBride, Dr. D. M. S. Watson, Dr. C. W. Andrews, and others.

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