age of the mother, and the number of previous children born to her, for all births completely registered. Unfortunately the number of previous children does not give exactly the parity of a birth, as some of the previous children may have resulted from multiple births. As the proportion of multiple maternities to all maternities seldom exceeds 2 per cent., the consequent lack of precision is not likely to lead to serious error in most applications, though from the point of view of this enquiry it is of greater significance. Included in the Registrar-General's Statistical Review for 1938 (Tables. Part II: Civil) there is a discussion of the first half-year's experience as it affects the problem of twinning. The numbers are frequently too small to provide more than an indication of the pattern of twin production, but since that time data for ten more years have been published.