Complex sentence: He exhibited regularly at the National Academy of Design, showing paintings in 1891,1893,1905,1906 and 1907 before he first showed his sculpture there, in 1908 and annually for many years, usually of portrait busts.
Split into simpler sentences: He exhibited regularly at the National Academy of Design, showing paintings in 1891,1893,1905,1906 and 1907. He first showed his sculpture there in 1908, and annually for many years, usually of portrait busts.