Abstract: Two monkeys were trained successfully to judge the numerousness of sides of polygons. In experiment 1, with the number of sides or angles of regularpolygons as numerousness discriminada,the best performance of the first mon-key was to meet the criterion (two successive sessions of 80% or more cor-rect) on the task 7 vs. 8 sides, the 2nd best was on the 6 vs. 7 task. Inexperiment 2, with the number of sides or angles of irregular polygons ascues, the best performance of the first monkey was on the 6 vs. 7 task, the2nd best was on the 5 vs 6 task

Key words: rhesus monkey, number of sides of polygon, number capacity in animals, the limits of numerousness discrimination