Image of Tower. The Tower test setup consisted of a 230-cm high cabinet with a transparent Plexiglas front, in which five horizontally situated crossbars with varying distances between 10, 19, 45, 70 and 50 cm, respectively. At the start of a test, a marmoset was located behind a sliding door adjacent to the bottom of the cabinet. After opening of the sliding door, the marmoset enters the cabinet. Simultaneously, an observer sitting in another room in front of a video screen recorded each point of time the marmoset jumped from one level to another over a 10-min period. The figure shows a marmoset at level 3 (A) and jumping (B) to level 5 (C).