Where surplus months exist, there is no intercalation in the proper sense, although the same name, e. g. the ‘harvest month’, will recur sometimes after 12, sometimes after 13 months, since owing to the fluctuating and unstable nature of the naming of the months the latter are distributed according to circumstances[925]. This covers the difficulty. Such seems to have been the state of affairs in the pre-Sargonic period at Lagash. Certainly Kugler (II, 216) has tried to demonstrate intercalary years: this is possible in the sense given above, but actually very uncertain, since the starting-points for the arrangement of the months are anything but certain[926]. Only the arising of a fixed series of months makes a genuine intercalation possible, since as a rule the general custom is to intercalate a definite month (in Babylonia, at least later, there were two such months, _adarru_ and _ululu_). The process is either an omission of one month in the series of thirteen, or an intercalation of one month in the series of twelve. The former appears in Lagash in the time of Sargon, the latter in the time of Dungi. We have found that the intercalation among the primitive peoples takes place as need arises. If the series of months is fixed, but the intercalation is neglected, the months must get out of place in relation to the seasons: this can be demonstrated in a couple of cases. So if the translation of the name of the fourth month in the list from Lagash is correct--_šu-kul-na_, ‘sowing month’--the harvest month, _še-kin-kud_, is the twelfth, and is therefore at a distance of eight months instead of the five which the natural conditions shew[927]. Further the list at the time of Dungi shews a disarrangement of the months as compared with the Sargonic list, the tenth month having dropped out and the following months being now pushed one place forwards. This difference can be explained either by a neglect of the intercalation, or by the fluctuating nature of the nomenclature: in the latter case there is really no genuine intercalation.