The fresh-waters of Japan afford a wonderful opportunity for the enthusiastic microscopist. Conditions under which simple organisms thrive are not wanting anywhere in that country. Flooded rice fields of the lowlands, cool mountain streams and innumerable lakes, large and small, are teeming with low plant and animal forms. To what extent systematic study of the microscopic fauna and flora of the waters of Japan has progressed, under the direction of the eminent biologists of that country, the writers of this article are not able to state. With a view of determining the species of Protozoa characteristic of Japan and comparing them with the American forms, microscopic studies were carried on by C. H. Edmondson during July and August, I912, in various parts of the main island. Beginning with Kobe, observations were made through the central and eastern sections of the country and as far north as Lake Chuzenji.