albiguttus, 14 cm. long, individual (B), on black and white background (2 mm. squares) from July 29, 11 a.m. to July 30, 3 p.m., after having been adapted to the background shown in figure 10. This indiviidual was extensively used in the study of adaption on artificial backgrounds. It is represented in many....figures. Note that numerous dark spots have appeared in the light areas shown in figure 10, and that the light spots in the dark areas have become more numerous and more conspicuous. 10- Individual (B) on black and white backgroune (5 mm. squares) from July 25, 2 p.m. to jUly 26, 11:30 a.m., after having been adapted to a white background. Note that the three very light gray areas around the ocelli...have become much darker and other dark spots have appeared. 11-Individual (B) on black and white backgroune (2 cm. squares) from August 1, 9 a.m., to 4:30 p.m., after having been adapted to 1 cm. squares, shown in figure 12. Note that the pattern has changed very little.12-Individual (B) opn black and white backgroune (1 cm. squares) from July 31, 11:40 a.m., to August 1, 9 a.m., after having been on (1 sq. cm. circles) from July 30, 3 p.m.., to July 31, 11:40 a.m. Note that the dark areas are darker than in figure 10..