Complex sentence: In 1905-06 he made a careful study of the pygmy races of Central Africa, and made investigations in the Philippine Islands in 1908, in Japan in 1909-10, and in Korea in 1911.
Split into simpler sentences: In 1905-06 he made a study of the pygmy races of Central Africa. In 1908 he did field work in the Philippine Islands, followed by Japan in 1909-10, and Korea in 1911.