From these indications of relative ages there arises of itself a familiar chronological expedient usually found at the point where history begins, viz. the reckoning by generations, which is common e. g. among the Polynesians[434] and in the older Greek historians. Among the Masai an elaborate system for classifying ages has exceptionally developed. The circumcision takes place in four-year periods with intervals of three and a half years. The circumcisions are known alternately as ‘right-hand’ and ‘left-hand’. Those who have been circumcised at the same time have a special name, such as ‘those who fight openly or by day’, ‘those who are not driven away’, etc.; one ‘right-hand’ and one ‘left-hand’ period combine to form a generation. The ‘those-who-fight-openly’ period is a ‘right-hand’ period, and those who belong to it were circumcised in 1851-5; the ‘those-who-are-not-driven-away’ period is a ‘left-hand’, and its members were circumcised in 1859-63. The two periods or ages together form a generation composed of persons born from 1834-1850. Each age has three divisions, first those known as ‘the big ostrich feathers’, secondly those called ‘the helpers’, and thirdly those known as ‘our fleet runners’[435]. It is evident that an excellent basis for the determination of relative time is hereby given. With time-reckoning _per se_ the system is not concerned. Common bases for reckoning are afforded by important and striking events which have been impressed upon everyone and are present to all men’s minds: through their relation to the age of some person they serve as a guide to the chronology. The Aino, for example, do not count the days, but always refer to events; if it is asked how old anyone is, the answer will be that he was born after the catching of the very big fish, or perhaps in the year when there was so much snow[436]. Here once more we see how concrete time-indications always precede the abstract numerical counting of time. And where numbers are known they are not willingly used, but the year is referred to as one distinguished by a certain noteworthy event, instead of being regarded as a member of a series. From a year of this kind the natives can only reckon for a few years at most in either direction. Where there are many such noteworthy years the time-relationship is so far recognised that the succession of the events is known, and perhaps in certain cases also forms the basis of calculation.