GLOBAL VERSIONS OF THE CENTRAL LIMIT THEOREM

changes between X and the short arm of the Y. This might likewise be interpreted as "protection," with the possibility in this case that the "protected" short arm might have a high frequency of exchange with the long arm. Investigations of exchanges with free or with attached. arms of the Y chromosome should be of value in answering some of the questions raised. Summary.-In attached-X females-lacking a Y chromosome, most of the induced detachments involve exchanges with chromosome 4. The presence of a Y chromosome increases the frequency of induced detachment, 80 per cent or more of the cases resulting from exchanges between X and Y. With only Ys present, there is a much greater increase in detachment frequency. It is suggested that the long arm of the Y "protects" the short arm against induced exchanges with the X and possibly vice versa. With sc8. Y, SC. yL, or scat YS, there is a marked reduction in the frequency of exchanges between attached X's and chromosome 4. This reduction is not obtained with yLC possibly due to its shape or to its lack of the proximal part of Ys.