Complex sentence: By 1941, he had his own solo series, "Captain Marvel Adventures", while he continued to appear in "Whiz Comics", as well as periodic appearances in other Fawcett books, including "Master Comics".
Split into simpler sentences: By 1941, he had his own solo series, "Captain Marvel Adventures", while continuing to appear in "Whiz Comics" as well. He also made periodic appearances in other Fawcett books, including "Master Comics".