All of my dancers had black eyes and were smaller as well as weaker than the albino mouse and the gray house mouse. The weakness indicated by their inability to hold up their own weight or to cling to an object curiously enough does not manifest itself in their dancing; in this they are indefatigable. Frequently they run in circles or whirl about with astonishing rapidity for several minutes at a time. Zoth (31 p. 173), who measured the strength of the dancer in comparison with that of the common mouse, found that it can hold up only about 2.8 times its own weight, whereas the common white mouse can hold up 4.4 times its weight. No other accurate measurements of the strength, endurance, or hardiness of the dancer are available. They are usually supposed to be weak and delicate, but my own observations cause me to regard them as exceptionally strong in certain respects and weak in others. [Illustration: FIGURE I.--Typical markings of dancers. A, blank outline of mouse for record. B, markings of No. 2 [symbol for male], born September 7, 1905, of unknown parents, died March 30,1907. C, markings of No 43 [symbol for female], born November 10, 1906, of 212 and 211. D, markings of No. 151 [symbol for female], born February 28, 1906, of 1000 and 5, died February 26, 1907.] What the Japanese have to say about the dancing mouse is of special importance because Japan is rather commonly supposed to be its home. For this reason, as well as because of the peculiar interest of the facts mentioned, I quote at length from Doctor Kishi (21 p. 457). "The dancing mouse has received in Europe this name which it does not bear in its own home, because of the fact that the circular movements which it makes are similar to the European (human) dance. Sometimes it is also called the Japanese or Chinese mouse; originally, however, China must have been its home, since in Japan it is mostly called '_Nankin nesumi_,' the mouse from Nankin. When this animal came from China to Japan I shall inquire at a later opportunity. There were originally in Japan two different species of mouse, the gray and the white; therefore in order to distinguish our dancing mouse from these it was necessary to use the name of its native city.