This report differs from earlier ones because financial limitations require the length to be half that of the preceding one. Thus, bibliographical lists are severely limited and it has not been possible to refer to all published papers or to much of the unpublished work. It is hoped that a more extensive mimeographed report will be available to commission members and others interested by the time of the 1970 General Assembly.

For invaluable aid in preparing this report, I am deeply indebted to Drs. Batten, Herczeg, Katherine Kron, Larsson-Leander, Merrill, Plavec, and Cesevič. Most of these wrote sections of the report which appear only slightly altered to prevent duplication or to take account of very recent developments. Since it was necessary to review more than 1400 papers which appeared during the three-year interval, obviously this could not have been written without extensive collaboration. I am especially indebted to Drs. Merrill and Plavec for consultation in the difficult choice of matters to be eliminated.