colors, but the effort was successful only to the extent that it was an improvement on its predecessors; and, although still the standard of color nomenclature among zoologists and many other naturalists, it nevertheless is seriously defective in the altogether inadequate number of colors represented, and in their unscientific arrangement. Fully realizing his failure, the author, some two or three years later, began to devise plans, gather materials, and acquire special knowledge of the subject, in the hope that he might some day be able to prepare a new work which would fully meet the needs of all who have use for it. Unfortunately, his time has been so fully occupied with other matters that progress has necessarily been slow; but after more than twenty years of sporadic effort it has at last been completed.
Acknowledgments are due to so many friends for helpful suggestions that it is hardly possible to name them all, or to specify the extent or kind of help which each has rendered; but special mention should be made of Mr. Lewis E. Jewell, of Johns Hopkins University; Dr. R. M. Strong, of the University of Chicago; Prof. W. J. Spillman, of the U. S. Department of Agriculture; Mr. Williams Welch, of the U. S. Signal Service; Mr. Milton Bradley, of Springfield, Mass.; Dr. P. G. Nutting, of the U. S. Bureau of Standards; Mr. P. L. Ricker, of the Bureau Of Plant Industry, U. S. Department of Agriculture; and Mr. J. L. Ridgway, of the U. S. Geological Survey. The late Professor S. P. Langley, then Secretary of the Smithsonian Institution, was good enough to take a kindly interest in this undertaking and gave the author assistance for which he is glad to make acknowledgment. More than to all others, however, is the author deeply indebted to Mr. John E. Thayer, of Lancaster, Mass., and Senor Don Jose C. Zeeedon, of San Jose, Costa Rica, for aid so indispensable that without it the work could not have been completed.
To Dr. G. Grubeer & Co., of Leipzig, Germany, the author is under obligations for the gift of a nearly complete set of their celebrated coal-tar dyes, which have proven quite necessary to the work, especially in the coloring of the Maxwell disks on which the color scheme is based.
The reproduction of the plates has been a difficult matter, involving not only expensive experimentation, but more than three
