I am very grateful for the invitation of the Association to speak about the work I have been doing with twins, as it is an opportunity to thank the very many members who have helped in it. Without your kindness and co-operation the work would not have been possible. Medical Superintendents have put themselves out to make it possible for me to see patients and examine records; medical officers have discussed cases with me; I have been able to see the invaluable reports on family visits by social workers, and P.S.W's. have even made special inquiries on my behalf; hospital secretaries have made visiting books and other records available, and have rummaged through dusty files for ancient case-notes, and they have added to their labours routine inquiries about twinship which have considerably enlarged my series. This help has been given not only to me personally, but also to other workers collaborating with me. For all this and more, which I have no time to mention, I want to say thank you very much.