From the Introduction ... 'A main theme of eusociality is division of labor (Wilson 1971, 1975), which can be based on physiological differences (as in the case of the reproductive queen and sterile workers), morphological (size) differences among workers, or age differences within a physical class. In social insects both age and physical classes can comprise castes, that is, groups of individuals which perform specialized labor for sustained periods of time (physical castes: Oster and Wilson, 1978; Wilson, 1980a,b; Herbers, 1980; age castes: Oster and Wilson, 1978; Porter and Jorgenson, 1981; Mirenda and Vinson, 1981; Seeley, 1982). We constructed an ethogram for the Indo-Australian ant Pheidole hortensis, and tested the general hypothesis of division of labor in the worker caste by seeking to answer these questions: 1. Is there division of labor between physical castes? 2. Is there division of labor among age classes within a physical caste? 3.And if there is age polyethism, is it continuous or discrete? (See Wilson 1976a.)We will consider and discuss each question separately, and then compare our results with those from other studies on social insects. In particular we will contrast age polyethism in Pheidole hortensis with that of a New World Pheidole species, P. dentata.'